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CVE-2026-54911

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.
Lifecycle PUBLISHED1 preserved revisionFact urn:baitaphish:canonical-cve-fact-revision:v2:c9a86a74d1c14183c5f86b700a58298a750900baf0e284bd090c5e1e64a2f4e4
Known exploited
Not asserted
Disputed
No
Stale source
No
Conflicts
0

Affected products and versions

1 source assertion
{"product":"ultrajson","vendor":"ultrajson","versions":[{"status":"affected","version":"< 5.13.0"}]}
  • cve_program_cvelist_v5affected
    urn:baitaphish:normalized-source-record:v2:8828bf7aa5664e702e38268d04da1f8640febd1e588e6514c42ce032f04af99e · sha256:3487d3ea93823dec… · /containers/cna/affected/0

Provider-owned CVSS observations

1 source assertion
{"metric":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":6.5,"baseSeverity":"MEDIUM","confidentialityImpact":"LOW","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","version":"3.1"},"metric_type":"cvssV3_1"}
  • cve_program_cvelist_v5cvss
    urn:baitaphish:normalized-source-record:v2:8828bf7aa5664e702e38268d04da1f8640febd1e588e6514c42ce032f04af99e · sha256:3487d3ea93823dec… · /containers/cna/metrics/0/cvssV3_1

CWE assertions

1 source assertion
{"cweId":"CWE-20","description":"CWE-20: Improper Input Validation","lang":"en","type":"CWE"}
  • cve_program_cvelist_v5cwe
    urn:baitaphish:normalized-source-record:v2:8828bf7aa5664e702e38268d04da1f8640febd1e588e6514c42ce032f04af99e · sha256:3487d3ea93823dec… · /containers/cna/problemTypes/0/descriptions/0

Source references

3 source assertions
{"name":"https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf","tags":["x_refsource_MISC"],"url":"https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:8828bf7aa5664e702e38268d04da1f8640febd1e588e6514c42ce032f04af99e · sha256:3487d3ea93823dec… · /containers/cna/references/1
{"name":"https://github.com/ultrajson/ultrajson/releases/tag/5.13.0","tags":["x_refsource_MISC"],"url":"https://github.com/ultrajson/ultrajson/releases/tag/5.13.0"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:8828bf7aa5664e702e38268d04da1f8640febd1e588e6514c42ce032f04af99e · sha256:3487d3ea93823dec… · /containers/cna/references/2
{"name":"https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2","tags":["x_refsource_CONFIRM"],"url":"https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2"}
  • cve_program_cvelist_v5reference
    urn:baitaphish:normalized-source-record:v2:8828bf7aa5664e702e38268d04da1f8640febd1e588e6514c42ce032f04af99e · sha256:3487d3ea93823dec… · /containers/cna/references/0

Attribution and limitations

  • CVE Program CVEList V5: Reproduce the MITRE copyright designation and CVE license in copies. Source →

Provider severity values are preserved separately. Baitaphish does not convert them into a risk rating, infer affected products, or treat EPSS as observed exploitation.

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