CVE-2022-31116: Incorrect handling of invalid surrogate pair characters in ujson

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.5% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2022-07-05 · updated 2026-06-17
Weakness: CWE-670

Description

UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Affected versions were found to improperly decode certain characters. 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. All users parsing JSON from untrusted sources are vulnerable. 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. Users are advised to upgrade. There are no known workarounds for this issue.

Affected products

Fedoraproject Fedora: 35, 36
ultrajson: before 5.4.0 — fixed in 5.4.0

How to fix

Upgrade to a fixed version: ultrajson 5.4.0. Check the vendor advisory for mitigations.

References

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