# What is CVE-2021-27853? > CVE-2021-27853 is a medium-severity flaw (CVSS 4.7) in Ieee 802.2, published on 27 September 2022. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 0.8%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-27853 ## At a glance - **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle. - **Precursor Intelligence risk score:** 44 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes. - **Severity:** Medium (CVSS 4.7 out of 10) - **Known to be exploited:** No, not on the list of flaws known to be exploited today - **Chance of use in the next 30 days:** 0.8% (latest exploit-likelihood forecast) - **Published:** 27 September 2022 - **Record last updated:** 4 November 2025 - **Main product:** Ieee 802.2 - **Affected products:** 96 ## What is CVE-2021-27853? In plain terms An attacker has to be on the same local network without logging in, and nobody has to click anything. If it works, the attacker can change some data. ### The official description Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using combinations of VLAN 0 headers and LLC/SNAP headers. ### What kind of flaw is it? - CWE-290: Authentication Bypass by Spoofing ### How an attack on it works - Where an attacker can be: On the same local network - How hard it is to pull off: Easy: no special conditions - Login needed first: No login needed - Does someone have to click: No, nobody has to do anything - What an attacker gets: Can change some data Severity vector: `CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N` ## Is CVE-2021-27853 being exploited? Not that we know of It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.8%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 0.8%, 0.8%, 0.8%, 0.8%, 0.8%, 0.8%, 0.8%. ### Timeline - 27 September 2022: Published - 4 November 2025: Record last updated ### How Precursor Intelligence ranks it CVE-2021-27853 scores **44 out of 100 (Medium)**, with the action "Plan remediation". Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less: - Evidence it is being exploited: biggest factor - How severe it is: strong factor - How widely exposed it is: smaller factor - Threat activity around it: smaller factor 85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it. ## Who is affected by CVE-2021-27853? The published record lists 96 products. - [Ieee 802.2](https://www.precursorintelligence.com/product/ieee/ieee_802.2) by [Ieee](https://www.precursorintelligence.com/vendors/ieee) (Application): up to 802.2h-1997 - [IOS XE](https://www.precursorintelligence.com/product/cisco/ios_xe) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Application): 15.2(07)e02, 15.2(07)e03, 17.3.3, 17.4.1, 17.6.1 - [Catalyst 6503-E Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6503-e_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6504-E Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6504-e_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6506-E Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6506-e_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6509-E Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6509-e_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6509-Neb-a Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6509-neb-a_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6509-V-E Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6509-v-e_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6513-E Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6513-e_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6800ia Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6800ia_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6807-Xl Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6807-xl_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6840-X Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6840-x_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst 6880-X Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_6880-x_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst C6816-X-Le Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_c6816-x-le_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst C6824-X-Le-40g Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_c6824-x-le-40g_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst C6832-X-Le Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_c6832-x-le_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Catalyst C6840-X-Le-40g Firmware](https://www.precursorintelligence.com/product/cisco/catalyst_c6840-x-le-40g_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 15.5(01.01.85)sy07 - [Meraki Ms210 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms210_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms225 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms225_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms250 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms250_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms350 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms350_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms355 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms355_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms390 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms390_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms410 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms410_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms420 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms420_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms425 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms425_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [Meraki Ms450 Firmware](https://www.precursorintelligence.com/product/cisco/meraki_ms450_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): version not specified - [N9k-C9316d-Gx Firmware](https://www.precursorintelligence.com/product/cisco/n9k-c9316d-gx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-C9332d-Gx2b Firmware](https://www.precursorintelligence.com/product/cisco/n9k-c9332d-gx2b_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-C9348d-Gx2a Firmware](https://www.precursorintelligence.com/product/cisco/n9k-c9348d-gx2a_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-C93600cd-Gx Firmware](https://www.precursorintelligence.com/product/cisco/n9k-c93600cd-gx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-C9364d-Gx2a Firmware](https://www.precursorintelligence.com/product/cisco/n9k-c9364d-gx2a_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9432c-S Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9432c-s_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9464px Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9464px_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9464tx2 Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9464tx2_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9564px Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9564px_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9564tx Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9564tx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9636c-R Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9636c-r_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9636c-Rx Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9636c-rx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X97160yc-EX Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x97160yc-ex_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9732c-EX Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9732c-ex_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9732c-Fx Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9732c-fx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9736c-EX Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9736c-ex_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9736c-Fx Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9736c-fx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [N9k-X9788tc-Fx Firmware](https://www.precursorintelligence.com/product/cisco/n9k-x9788tc-fx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 92160yc-X Firmware](https://www.precursorintelligence.com/product/cisco/nexus_92160yc-x_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 92300yc Firmware](https://www.precursorintelligence.com/product/cisco/nexus_92300yc_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 92304qc Firmware](https://www.precursorintelligence.com/product/cisco/nexus_92304qc_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 92348gc-X Firmware](https://www.precursorintelligence.com/product/cisco/nexus_92348gc-x_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9236c Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9236c_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9272q Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9272q_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93108tc-EX Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93108tc-ex_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93108tc-Fx Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93108tc-fx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93108tc-Fx3p Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93108tc-fx3p_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93120tx Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93120tx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93180yc-EX Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93180yc-ex_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93180yc-Fx Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93180yc-fx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93180yc-Fx3 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93180yc-fx3_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93216tc-Fx2 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93216tc-fx2_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93240yc-Fx2 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93240yc-fx2_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9332c Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9332c_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 93360yc-Fx2 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_93360yc-fx2_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9336c-Fx2 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9336c-fx2_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9336c-Fx2-E Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9336c-fx2-e_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9348gc-Fxp Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9348gc-fxp_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9364c Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9364c_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9364c-Gx Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9364c-gx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9432pq Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9432pq_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9504 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9504_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9508 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9508_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9516 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9516_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9536pq Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9536pq_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9636pq Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9636pq_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9716d-Gx Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9716d-gx_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9736pq Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9736pq_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus 9800 Firmware](https://www.precursorintelligence.com/product/cisco/nexus_9800_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [Nexus X9636q-R Firmware](https://www.precursorintelligence.com/product/cisco/nexus_x9636q-r_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 9.3(5) - [P802.1q](https://www.precursorintelligence.com/product/ietf/p802.1q) by [Ietf](https://www.precursorintelligence.com/vendors/ietf) (Application): up to d1.0 - [Sf-500-24mp Firmware](https://www.precursorintelligence.com/product/cisco/sf-500-24mp_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sf500-18p Firmware](https://www.precursorintelligence.com/product/cisco/sf500-18p_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sf500-24 Firmware](https://www.precursorintelligence.com/product/cisco/sf500-24_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sf500-24p Firmware](https://www.precursorintelligence.com/product/cisco/sf500-24p_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sf500-48 Firmware](https://www.precursorintelligence.com/product/cisco/sf500-48_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sf500-48mp Firmware](https://www.precursorintelligence.com/product/cisco/sf500-48mp_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500-28 Firmware](https://www.precursorintelligence.com/product/cisco/sg500-28_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500-28mpp Firmware](https://www.precursorintelligence.com/product/cisco/sg500-28mpp_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500-28p Firmware](https://www.precursorintelligence.com/product/cisco/sg500-28p_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500-52 Firmware](https://www.precursorintelligence.com/product/cisco/sg500-52_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500-52mp Firmware](https://www.precursorintelligence.com/product/cisco/sg500-52mp_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500-52p Firmware](https://www.precursorintelligence.com/product/cisco/sg500-52p_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500x-24 Firmware](https://www.precursorintelligence.com/product/cisco/sg500x-24_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500x-24mpp Firmware](https://www.precursorintelligence.com/product/cisco/sg500x-24mpp_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500x-24p Firmware](https://www.precursorintelligence.com/product/cisco/sg500x-24p_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500x-48 Firmware](https://www.precursorintelligence.com/product/cisco/sg500x-48_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500x-48mpp Firmware](https://www.precursorintelligence.com/product/cisco/sg500x-48mpp_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 - [Sg500x-48p Firmware](https://www.precursorintelligence.com/product/cisco/sg500x-48p_firmware) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Operating system): 3.0.0.61 ## How do I fix CVE-2021-27853? 1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list. 2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list. 3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in. 4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood. ### References - [standards.ieee.org](https://standards.ieee.org/ieee/802.1Q/10323/) (Vendor advisory) - [standards.ieee.org](https://standards.ieee.org/ieee/802.2/1048/) (Vendor advisory) - [blog.champtar.fr](https://blog.champtar.fr/VLAN0_LLC_SNAP/) (Exploit, Third-party advisory) - [datatracker.ietf.org](https://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/) (Technical description, Third-party advisory) - [kb.cert.org](https://kb.cert.org/vuls/id/855201) (Third-party advisory, Government resource) - [tools.cisco.com](https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX) (Third-party advisory) ## Questions ### What is CVE-2021-27853? CVE-2021-27853 is a medium-severity flaw in Ieee 802.2, published on 27 September 2022. An attacker has to be on the same local network without logging in, and nobody has to click anything. If it works, the attacker can change some data. ### How serious is CVE-2021-27853? It scores 4.7 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2021-27853 is 44 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle. ### Is CVE-2021-27853 being exploited? It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.8%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2021-27853 affect? For Ieee 802.2: up to 802.2h-1997. The record lists 96 products in all, each with its versions, under "Who is affected" on this page. ### How do I fix CVE-2021-27853? Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. ## Does CVE-2021-27853 affect you? Precursor Intelligence keeps checking for you: - **Tell us what you run.** Pick your software from a list, or let us work it out from your website. - **We match it to every flaw.** Over 400,000 published flaws, checked against your list. - **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it. - **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools. Start free (no card, nothing to install): https://www.precursorintelligence.com/register Book a demo: https://www.precursorintelligence.com/contact