Vulnerability in ujson (CVE-2026-54911)
Summary
Vulnerability in ujson (CVE-2026-54911). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 5.13.0 or later.
Original description
The description as published by the source.
UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.13.0, ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. This vulnerability is fixed in 5.13.0.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-54911 has been found in ujson.
Risk of unauthorized operations or information disclosure. CVSS score: 6.5/10.
What to do: upgrade ujson to 5.13.0 or later.
If unsure, ask your IT team or search "ujson CVE-2026-54911" on the vendor's site.
CVE-2026-54911 (ujson) — CWE-20 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 5.13.0 — apply immediately
Workaround: Decoding bytes to strings in Python before passing them to ujson.dumps() avoids this issue.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-20) exists in ujson.
Check the vendor advisory for the affected versions of ujson.
Severity: Medium (CVSS 6.5/10). Risk of unauthorized operations or information disclosure.
Update to 5.13.0.
Workaround: Decoding bytes to strings in Python before passing them to ujson.dumps() avoids this issue.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'ujson' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'ujson' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
ujsonを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
Decoding bytes to strings in Python before passing them to `ujson.dumps()` avoids this issue.パッチが適用されるまでの応急処置として、Decoding bytes to strings in Python before passing them to
ujson.dumps()avoids this issue. を実施。回避策の副作用 (機能低下) を確認した上で。 -
3Apply patch patch
Upgrade ujson to 5.13.0ステージング環境で 5.13.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
4Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-54911 ujson
- Ubuntu UBUNTU-CVE-2026-54911 pandas
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- patch github.com
- web github.com
- web github.com
- web github.com