lxml NULL Pointer Dereference allows attackers to cause a denial of service

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2022-2309: 2.45% estimated exploitation activity in the next 30 days; percentile 84.39 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

NULL Pointer Dereference allows attackers to cause a denial of service (or application crash). This only applies when lxml is used together with libxml2 2.9.10 through 2.9.14. libxml2 2.9.9 and earlier are not affected. It allows triggering crashes through forged input data, given a vulnerable code sequence in the application. The vulnerability is caused by the iterwalk function (also used by the canonicalize function). Such code shouldn't be in wide-spread use, given that parsing + iterwalk would usually be replaced with the more efficient iterparse function. However, an XML converter that serialises to C14N would also be vulnerable, for example, and there are legitimate use cases for this code sequence. If untrusted input is received (also remotely) and processed via iterwalk function, a crash can be triggered.

Published by the source

6 Jul 2022, 00:00 UTC

Last modified by the source

4 Nov 2025, 20:44 UTC

Source last checked

26 Oct 2026, 13:35 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-wrxv-2j5q-m38w

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-wrxv-2j5q-m38w

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# Patch Next advisory brief: CVE-2022-2309

Advisory: lxml NULL Pointer Dereference allows attackers to cause a denial of service
IDs: CVE-2022-2309, GHSA-wrxv-2j5q-m38w
Record: https://patchnext.com/advisories/cve-2022-2309 (revision 3, source checked 26 Oct 2026, 13:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lxml 4.9.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI lxml: affected < 4.9.1; fixed in 4.9.1

## Suggested inspection (read-only)
- `python -m pip show lxml`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on lxml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wrxv-2j5q-m38w (OSV record GHSA-wrxv-2j5q-m38w lists affected ranges: PyPI lxml >=0 <4.9.1 (fixed))
- Verified: https://github.com/advisories/GHSA-wrxv-2j5q-m38w (GitHub-reviewed advisory GHSA-wrxv-2j5q-m38w lists affected ranges: PyPI lxml >=0 <4.9.1)

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