# What is CVE-2021-43527? > CVE-2021-43527 is a critical-severity flaw (CVSS 9.8) in Nss from Mozilla, published on 8 December 2021. 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 18%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-43527 ## At a glance - **Verdict:** Fix this soon. Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month. - **Precursor Intelligence risk score:** 55 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes. - **Severity:** Critical (CVSS 9.8 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:** 18% (latest exploit-likelihood forecast) - **Published:** 8 December 2021 - **Record last updated:** 23 February 2023 - **Main product:** Nss from Mozilla - **Affected products:** 10 ## What is CVE-2021-43527? In plain terms It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline. ### The official description NSS (Network Security Services) versions prior to 3.73 or 3.68.1 ESR are vulnerable to a heap overflow when handling DER-encoded DSA or RSA-PSS signatures. Applications using NSS for handling signatures encoded within CMS, S/MIME, PKCS \#7, or PKCS \#12 are likely to be impacted. Applications using NSS for certificate validation or other TLS, X.509, OCSP or CRL functionality may be impacted, depending on how they configure NSS. *Note: This vulnerability does NOT impact Mozilla Firefox.* However, email clients and PDF viewers that use NSS for signature verification, such as Thunderbird, LibreOffice, Evolution and Evince are believed to be impacted. This vulnerability affects NSS < 3.73 and NSS < 3.68.1. ### What kind of flaw is it? - CWE-787: Out-of-bounds Write ### How an attack on it works - Where an attacker can be: Anywhere on the internet - 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 read data, change data and take it offline Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` ## Is CVE-2021-43527 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 18%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 18%, 18%, 18%, 18%, 18%, 18%, 18%. ### Timeline - 8 December 2021: Published - 23 February 2023: Record last updated - 16 June 2026: Exploit likelihood jumped ### How Precursor Intelligence ranks it CVE-2021-43527 scores **55 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-2021-43527? The published record lists 10 products. Versions are as published: "before 3.73" means every version up to, but not including, 3.73. - [Nss](https://www.precursorintelligence.com/product/mozilla/nss) by [Mozilla](https://www.precursorintelligence.com/vendors/mozilla) (Application): before 3.73 - [Communications Cloud Native Core Network Repository Function](https://www.precursorintelligence.com/product/oracle/communications_cloud_native_core_network_repository_function) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 1.15.0, 1.15.1 - [Cloud Backup](https://www.precursorintelligence.com/product/netapp/cloud_backup) by [Netapp](https://www.precursorintelligence.com/vendors/netapp) (Application): version not specified - [Communications Cloud Native Core Binding Support Function](https://www.precursorintelligence.com/product/oracle/communications_cloud_native_core_binding_support_function) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 1.11.0 - [Communications Cloud Native Core Network Slice Selection Function](https://www.precursorintelligence.com/product/oracle/communications_cloud_native_core_network_slice_selection_function) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 1.8.0 - [Communications Policy Management](https://www.precursorintelligence.com/product/oracle/communications_policy_management) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 12.6.0.0.0 - [E-Series Santricity OS Controller](https://www.precursorintelligence.com/product/netapp/e-series_santricity_os_controller) by [Netapp](https://www.precursorintelligence.com/vendors/netapp) (Application): 11.0 to 11.70.1 - [Nss Esr](https://www.precursorintelligence.com/product/mozilla/nss_esr) by [Mozilla](https://www.precursorintelligence.com/vendors/mozilla) (Application): before 3.68.1 - Starwind SAN & NAS by [Starwindsoftware](https://www.precursorintelligence.com/vendors/starwindsoftware) (Application): v8r13 - [Starwind Virtual SAN](https://www.precursorintelligence.com/product/starwindsoftware/starwind_virtual_san) by [Starwindsoftware](https://www.precursorintelligence.com/vendors/starwindsoftware) (Application): v8r13-14398 ## How do I fix CVE-2021-43527? 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 - [oracle.com](https://www.oracle.com/security-alerts/cpuapr2022.html) (Patch, Third-party advisory) - [bugzilla.mozilla.org](https://bugzilla.mozilla.org/show_bug.cgi?id=1737470) (Issue tracking, Permissions required, Vendor advisory) - [ftp.mozilla.org](https://ftp.mozilla.org/pub/security/nss/releases/NSS_3_68_1_RTM/) (Vendor advisory) - [ftp.mozilla.org](https://ftp.mozilla.org/pub/security/nss/releases/NSS_3_73_RTM/) (Vendor advisory) - [mozilla.org](https://www.mozilla.org/security/advisories/mfsa2021-51/) (Vendor advisory) - [cert-portal.siemens.com](https://cert-portal.siemens.com/productcert/pdf/ssa-594438.pdf) (Third-party advisory) - [security.gentoo.org](https://security.gentoo.org/glsa/202212-05) (Third-party advisory) - [security.netapp.com](https://security.netapp.com/advisory/ntap-20211229-0002/) (Third-party advisory) - [starwindsoftware.com](https://www.starwindsoftware.com/security/sw-20220802-0001/) (Third-party advisory) ## Questions ### What is CVE-2021-43527? CVE-2021-43527 is a critical-severity flaw in Nss from Mozilla, published on 8 December 2021. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline. ### How serious is CVE-2021-43527? It scores 9.8 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2021-43527 is 55 out of 100, which is Medium. Its action is "Plan remediation". Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month. ### Is CVE-2021-43527 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 18%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2021-43527 affect? For Nss from Mozilla: before 3.73. The record lists 10 products in all, each with its versions, under "Who is affected" on this page. ### How do I fix CVE-2021-43527? 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-2021-43527 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