CVE-2026-54911

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Source
https://cve.org/CVERecord?id=CVE-2026-54911
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-54911.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-54911
Aliases
Downstream
Related
Published
2026-06-22T20:53:07.019Z
Modified
2026-07-15T15:52:59.094457Z
Severity
  • 6.5 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N CVSS Calculator
Summary
UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()
Details

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.

Database specific 
{
    "cwe_ids": [
        "CWE-20"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54911.json",
    "cna_assigner": "GitHub_M"
}
References

Affected packages

Git / github.com/ultrajson/ultrajson

Affected ranges

Type
GIT
Repo
https://github.com/ultrajson/ultrajson
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
1a23a68bbc5aff84e3f78f65011362cf3389693c
Fixed
169eaf36b1116fece5034ee79a7a0ef3f6deedcf
Database specific 
{
    "cpe": "cpe:2.3:a:ultrajson_project:ultrajson:*:*:*:*:*:python:*:*",
    "source": [
        "CPE_RANGE",
        "REFERENCES"
    ],
    "extracted_events": [
        {
            "introduced": "0"
        },
        {
            "fixed": "5.13.0"
        }
    ]
}

Affected versions

2.*
2.0.0
2.0.1
2.0.2
2.0.3
3.*
3.0.0
3.1.0
3.2.0
4.*
4.0.0
4.0.1
4.0.2
4.1.0
4.2.0
4.3.0
5.*
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
v1.*
v1.34
v1.35

Database specific

vanir_signatures_modified 
"2026-07-15T15:52:59Z"
vanir_signatures 
[
    {
        "signature_type": "Function",
        "target": {
            "file": "src/ujson/lib/ultrajsondec.c",
            "function": "decode_string"
        },
        "deprecated": false,
        "source": "https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf",
        "id": "CVE-2026-54911-1ba50fda",
        "signature_version": "v1",
        "digest": {
            "function_hash": "202621309646466819243650859435479759111",
            "length": 4707.0
        }
    },
    {
        "signature_type": "Function",
        "target": {
            "file": "src/ujson/lib/ultrajsonenc.c",
            "function": "Buffer_EscapeStringValidated"
        },
        "deprecated": false,
        "source": "https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf",
        "id": "CVE-2026-54911-605d024a",
        "signature_version": "v1",
        "digest": {
            "function_hash": "301418911564339236853002430134954153603",
            "length": 4363.0
        }
    },
    {
        "signature_type": "Line",
        "target": {
            "file": "src/ujson/lib/ultrajsonenc.c"
        },
        "deprecated": false,
        "source": "https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf",
        "id": "CVE-2026-54911-cf01a4e0",
        "signature_version": "v1",
        "digest": {
            "line_hashes": [
                "183356686465991657543968454615352760020",
                "216624396578935828529190988019428788737",
                "225986439972401945227232699573925747033",
                "239436793528923148022997059891535692684",
                "314169908770867073410235885105554691348",
                "61952369377442215753842942794814250060",
                "308396118214566931137410121468649898306",
                "78542097989186174125166363124376193288",
                "225629880217422800424367842891340668659",
                "19410481681690746784091377088539146070",
                "197157992881825332697941139432692290915",
                "24729007628964650252180500868647821073",
                "323818717674253734601967942692504240337",
                "58780892605965652217667193137527538039",
                "313392847737891028708223326163817585527",
                "278921498631358056901314484452377605914",
                "307328719378218029177167977555540508041",
                "328613520901764627977465256970068630797",
                "220099085178709560247011966194386339119",
                "6544109849124358725178157618573165670",
                "291850585735821742303304925047481620472",
                "225629880217422800424367842891340668659",
                "19410481681690746784091377088539146070",
                "197157992881825332697941139432692290915",
                "113165883423682887530862359483217953660",
                "308535338731952697559922003104541471776",
                "138159681411243518554119539526431104224",
                "35801856043602795738753192212980094344",
                "166791125187405989062185510977810929660",
                "202487193614678491504040639271766102413",
                "33847549388412089010167325700912793649",
                "196238276339567255954669125177791501250",
                "168971611491434606618324579192498797383",
                "296408806923738489611725998361220168582",
                "225629880217422800424367842891340668659",
                "19410481681690746784091377088539146070",
                "224215170243603256319363468638032920094",
                "309573676307503691532454082653554525814",
                "123373765476412738366787211044345708925",
                "263104866661036091654666963903361686346",
                "61244480925647787680873627755084990571",
                "6023633919025188748677291944149995304",
                "59995588160906581314279456833853792665"
            ],
            "threshold": 0.9
        }
    },
    {
        "signature_type": "Line",
        "target": {
            "file": "src/ujson/lib/ultrajsondec.c"
        },
        "deprecated": false,
        "source": "https://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf",
        "id": "CVE-2026-54911-ec576ef4",
        "signature_version": "v1",
        "digest": {
            "line_hashes": [
                "61481268627701308587471944238297797995",
                "255742195461137378269970914111607734063",
                "31225772365792635901844896752134988210",
                "211966799795300545858895841143077196764",
                "151747333764570602615526167634749269660",
                "262483871725234123578935494882417481646",
                "233957078391859710991655723075139422612",
                "339067184866058804308444017750064762913",
                "176383592832049596714502255493947393828",
                "242591874970349707558124265200327439585",
                "338029387652670975555658015067779412221",
                "332713471348858151646098004682020589953"
            ],
            "threshold": 0.9
        }
    }
]
source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-54911.json"