GHSA-3j69-69wj-xqx2 is a medium-severity (CVSS 6.5) vulnerability in ujson. A fix is available for ujson — see the affected versions and patch details below.
UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-3j69-69wj-xqx2.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-3j69-69wj-xqx2 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 374,847 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
ujsonReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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.
Details
The expected behavior is that for x being any bytes string, x == ujson.loads(ujson.dumps(x, reject_bytes=False)).encode(errors="surrogatepass") should always either be true or ujson.dumps() will throw an exception. In reality, some strings which should've been errors are silently rewritten as other strings:
- Invalid continuation bytes are replaced with valid ones:
b'\xcf\x13'->b'\xcf\x93' - Unterminated sequence completes the sequence:
b'\xc3'->b'\xc3\x80' - ... or leads to reading past the end of string:
b'\xf0\x90\x94'->b"\xf0\x90\x94\x80inxcontrib'"
Impact
An application relying on reject_bytes=False for UTF-8 handling may experience:
- Data integrity issues
- Experience validation bypass if said validation occurs before serialisation
Remediation
The missing/broken UTF-8 validation checks were added/fixed in https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf. We recommend upgrading to UltraJSON 5.13.0.
Workarounds
Decoding bytes to strings in Python before passing them to ujson.dumps() avoids this issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | ujson | all versions | 5.13.0pip install --upgrade 'ujson==5.13.0' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ujson, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ujson to 5.13.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3j69-69wj-xqx2 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-3j69-69wj-xqx2 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-3j69-69wj-xqx2. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-3j69-69wj-xqx2 in your dependencies?
O3 Security finds GHSA-3j69-69wj-xqx2 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.