# What is CVE-2021-43859? > CVE-2021-43859 is a high-severity flaw (CVSS 7.5) in Xstream, published on 1 February 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 7.9%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-43859 ## 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:** 50 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes. - **Severity:** High (CVSS 7.5 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:** 7.9% (latest exploit-likelihood forecast) - **Published:** 1 February 2022 - **Record last updated:** 3 November 2025 - **Main product:** Xstream - **Affected products:** 11 ## What is CVE-2021-43859? 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 take it offline. ### The official description XStream is an open source java library to serialize objects to XML and back again. Versions prior to 1.4.19 may allow a remote attacker to allocate 100% CPU time on the target system depending on CPU type or parallel execution of such a payload resulting in a denial of service only by manipulating the processed input stream. XStream 1.4.19 monitors and accumulates the time it takes to add elements to collections and throws an exception if a set threshold is exceeded. Users are advised to upgrade as soon as possible. Users unable to upgrade may set the NO_REFERENCE mode to prevent recursion. See GHSA-rmr5-cpv2-vgjf for further details on a workaround if an upgrade is not possible. ### What kind of flaw is it? - CWE-400: Uncontrolled Resource Consumption ### 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 take it offline Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H` ## Is CVE-2021-43859 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 7.9%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 7.9%, 7.9%, 7.9%, 7.9%, 7.9%, 7.9%, 7.9%. ### Timeline - 1 February 2022: Published - 3 November 2025: Record last updated - 19 November 2025: Exploit likelihood jumped - 22 November 2025: Exploit likelihood fell ### How Precursor Intelligence ranks it CVE-2021-43859 scores **50 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-2021-43859? The published record lists 11 products. Versions are as published: "before 1.4.19" means every version up to, but not including, 1.4.19. - [Xstream](https://www.precursorintelligence.com/product/xstream/xstream) by [Xstream](https://www.precursorintelligence.com/vendors/xstream) (Application): before 1.4.19 - [Retail Xstore Point of Service](https://www.precursorintelligence.com/product/oracle/retail_xstore_point_of_service) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 16.0.6, 17.0.4, 18.0.3, 19.0.2, 20.0.1 - [Communications Brm - Elastic Charging Engine](https://www.precursorintelligence.com/product/oracle/communications_brm_-_elastic_charging_engine) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): before 12.0.0.4.6, 12.0.0.5.0 - [Communications Diameter Intelligence Hub](https://www.precursorintelligence.com/product/oracle/communications_diameter_intelligence_hub) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 8.0.0 to 8.1.0, 8.2.0 to 8.2.6 - [Fedora](https://www.precursorintelligence.com/product/fedoraproject/fedora) by [Fedoraproject](https://www.precursorintelligence.com/vendors/fedoraproject) (Operating system): 34, 35 - [Jenkins](https://www.precursorintelligence.com/product/jenkins/jenkins) by [Jenkins](https://www.precursorintelligence.com/vendors/jenkins) (Application): before 2.319.3, 2.321 to before 2.334 - [Commerce Guided Search](https://www.precursorintelligence.com/product/oracle/commerce_guided_search) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 11.3.2 - [Communications Cloud Native Core Automated Test Suite](https://www.precursorintelligence.com/product/oracle/communications_cloud_native_core_automated_test_suite) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 1.9.0 - [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 - [Debian Linux](https://www.precursorintelligence.com/product/debian/debian_linux) by [Debian](https://www.precursorintelligence.com/vendors/debian) (Operating system): 9.0 - [Flexcube Private Banking](https://www.precursorintelligence.com/product/oracle/flexcube_private_banking) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 12.1.0 ## How do I fix CVE-2021-43859? 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 - [github.com](https://github.com/x-stream/xstream/commit/e8e88621ba1c85ac3b8620337dd672e0c0c3a846) (Patch, Third-party advisory) - [oracle.com](https://www.oracle.com/security-alerts/cpuapr2022.html) (Patch, Third-party advisory) - [oracle.com](https://www.oracle.com/security-alerts/cpujul2022.html) (Patch, Third-party advisory) - [x-stream.github.io](https://x-stream.github.io/CVE-2021-43859.html) (Exploit, Vendor advisory) - [openwall.com](http://www.openwall.com/lists/oss-security/2022/02/09/1) (Mailing list, Third-party advisory) - [github.com](https://github.com/x-stream/xstream/security/advisories/GHSA-rmr5-cpv2-vgjf) (Exploit, Third-party advisory) - [lists.debian.org](https://lists.debian.org/debian-lts-announce/2022/02/msg00018.html) (Mailing list, Third-party advisory) - [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VACQYG356OHUTD5WQGAQ4L2TTFTAV3SJ/) (Mailing list) - [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XODFRE2ZL64FICBJDOPWOLPTSSAI4U7X/) (Mailing list) - [lists.debian.org](https://lists.debian.org/debian-lts-announce/2024/12/msg00023.html) ## Questions ### What is CVE-2021-43859? CVE-2021-43859 is a high-severity flaw in Xstream, published on 1 February 2022. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can take it offline. ### How serious is CVE-2021-43859? It scores 7.5 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-43859 is 50 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-2021-43859 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 7.9%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2021-43859 affect? For Xstream: before 1.4.19. The record lists 11 products in all, each with its versions, under "Who is affected" on this page. ### How do I fix CVE-2021-43859? 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-2021-43859 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