6.9Medium
Xmlsoft Libxml2
CVE-2026-86143
In xmlIO in libxml2 before 2.15.4, an inconsistency in xmlOutputWriteCallback and xmlBufUse causes negative lengths to reach write callbacks, aka a lack of a check for integer overflow before calling writecallback. This has security relevance for many types of uses of that length value within a callback.
What this means for your business
- It affects Xmlsoft Libxml2. It matters if your company, or a supplier that handles your data, runs it.
- Code showing how to exploit it has been published, but real attacks have not been confirmed.
- An attacker can use it only with access to the machine itself, without a login, and without anyone at your company clicking anything.
- FIRST's prediction model gives it a 0.1% chance of attack attempts being seen in the next 30 days, ranking above 2% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Xmlsoft Libxml2, and which version. The affected versions are listed further down this page.
- 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
Not sure if your company is exposed?
Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.
Scoring
- CVSS
- 6.9 (v3.1)
- Vector
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L- Weakness
- CWE-192
- Assigned by
- cve@mitre.org
Dates
- Published
- 2026-09-05
- Last modified
- 2026-09-15
- Sources
- NVD
Affected products
- Xmlsoft Libxml2- 2.15.4
As listed in the NVD configuration data. Not a statement about your estate.