{"cve":"CVE-2026-54911","nvd":{"published":"2026-06-22T22:16:50.397","modified":"2026-06-26T20:10:54.850","status":"Analyzed","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","score":6.5},"cwes":["CWE-20"],"references":["https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf","https://github.com/ultrajson/ultrajson/releases/tag/5.13.0","https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2"],"products":["ultrajson_project:ultrajson"],"source":"nvd","synced_at":"2026-10-19T22:39:28.638635428+00:00"},"epss":{"cve":"CVE-2026-54911","score":0.00371,"percentile":0.31102,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-3j69-69wj-xqx2","url":"https://osv.dev/vulnerability/GHSA-3j69-69wj-xqx2","summary":"UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()","modified":"2026-09-10T03:50:55.310105853Z","packages":[{"ecosystem":"PyPI","name":"ujson","purl":"pkg:pypi/ujson","ranges":["<5.13.0"],"fixed":["5.13.0"]}]},{"id":"PYSEC-2026-2294","url":"https://osv.dev/vulnerability/PYSEC-2026-2294","summary":"","modified":"2026-07-13T07:15:45.403361942Z","packages":[{"ecosystem":"PyPI","name":"ujson","purl":"pkg:pypi/ujson","ranges":["<5.13.0"],"fixed":["5.13.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}