{"id":"GHSA-3j69-69wj-xqx2","summary":"UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()","details":"### Summary\n`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.\n\n### Details\n\nThe 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:\n\n* Invalid continuation bytes are replaced with valid ones: `b'\\xcf\\x13'` -\u003e `b'\\xcf\\x93'`\n* Unterminated sequence completes the sequence: `b'\\xc3'` -\u003e `b'\\xc3\\x80'`\n* ... or leads to reading past the end of string: `b'\\xf0\\x90\\x94'` -\u003e `b\"\\xf0\\x90\\x94\\x80inxcontrib'\"`\n\n### Impact\n\nAn application relying on reject_bytes=False for UTF-8 handling may experience:\n\n- Data integrity issues\n- Experience validation bypass if said validation occurs before serialisation\n\n### Remediation\n\nThe 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](https://github.com/ultrajson/ultrajson/releases/tag/5.13.0).\n\n### Workarounds\n\nDecoding bytes to strings in Python before passing them to `ujson.dumps()` avoids this issue.","aliases":["CVE-2026-54911","PYSEC-2026-2294"],"modified":"2026-07-18T17:45:18.566400173Z","published":"2026-06-19T20:47:43Z","database_specific":{"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-06-19T20:47:43Z","nvd_published_at":"2026-06-22T22:16:50Z","cwe_ids":["CWE-20"]},"references":[{"type":"WEB","url":"https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54911"},{"type":"WEB","url":"https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/ujson/PYSEC-2026-2294.yaml"},{"type":"PACKAGE","url":"https://github.com/ultrajson/ultrajson"},{"type":"WEB","url":"https://github.com/ultrajson/ultrajson/releases/tag/5.13.0"}],"affected":[{"package":{"name":"ujson","ecosystem":"PyPI","purl":"pkg:pypi/ujson"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.13.0"}]}],"versions":["1.15","1.18","1.19","1.21","1.22","1.23","1.30","1.33","1.34","1.35","1.4","1.6","1.8","1.9","2.0.0","2.0.1","2.0.2","2.0.3","3.0.0","3.1.0","3.2.0","4.0.0","4.0.1","4.0.2","4.1.0","4.2.0","4.3.0","5.0.0","5.1.0","5.10.0","5.11.0","5.12.0","5.12.1","5.2.0","5.3.0","5.4.0","5.5.0","5.6.0","5.7.0","5.8.0","5.9.0"],"database_specific":{"last_known_affected_version_range":"\u003c= 5.12.1","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-3j69-69wj-xqx2/GHSA-3j69-69wj-xqx2.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"}]}