Incorrect handling of invalid surrogate pair characters
Impact
What kind of vulnerability is it? Who is impacted?
Anyone parsing JSON from an untrusted source is vulnerable.
JSON strings that contain escaped surrogate characters not part of a proper surrogate pair were decoded incorrectly. Besides corrupting strings, this allowed for potential key confusion and value overwriting in dictionaries.
Examples:
# An unpaired high surrogate character is ignored.
>>> ujson.loads(r'"\uD800"')
''
>>> ujson.loads(r'"\uD800hello"')
'hello'
# An unpaired low surrogate character is preserved.
>>> ujson.loads(r'"\uDC00"')
'\udc00'
# A pair of surrogates with additional non surrogate characters pair up in spite of being invalid.
>>> ujson.loads(r'"\uD800foo bar\uDC00"')
'foo bar𐀀'Patches
Has the problem been patched? What versions should users upgrade to?
Users should upgrade to UltraJSON 5.4.0.
From version 5.4.0, UltraJSON decodes lone surrogates in the same way as the standard library's json module does, preserving them in the parsed output:
>>> ujson.loads(r'"\uD800"')
'\ud800'
>>> ujson.loads(r'"\uD800hello"')
'\ud800hello'
>>> ujson.loads(r'"\uDC00"')
'\udc00'
>>> ujson.loads(r'"\uD800foo bar\uDC00"')
'\ud800foo bar\udc00'Workarounds
Is there a way for users to fix or remediate the vulnerability without upgrading?
Short of switching to an entirely different JSON library, there are no safe alternatives to upgrading.
For more information
If you have any questions or comments about this advisory:
- Open an issue in UltraJSON
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | ujson | < 5.4.0 | 5.4.0 |
References
- https://github.com/ultrajson/ultrajson/security/advisories/GHSA-wpqr-jcpx-745r
- https://nvd.nist.gov/vuln/detail/CVE-2022-31116
- https://github.com/ultrajson/ultrajson/commit/67ec07183342589d602e0fcf7bb1ff3e19272687
- https://github.com/ultrajson/ultrajson
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NAU5N4A7EUK2AMUCOLYDD5ARXAJYZBD2
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/OPPU5FZP3LCTXYORFH7NHUMYA5X66IA7
- https://pypi.org/project/ujson
- https://github.com/advisories/GHSA-wpqr-jcpx-745r
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-670- Platform
- Python (PyPI)
- Package
ujson- Disclosed
- 05.07.2022
- Updated
- 11.10.2026 13:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1057 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-wpqr-jcpx-745r - CC BY 4.0
Vulnerability history: ujson
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 7
- First → latest
- 01.2022 06.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Medium 3
Disclosures per year
- 2022: 3
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 4
-
Incorrect handling of invalid surrogate pair characters this entry
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