Description
UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.12.1, when ujson.dump() writes to a file-like object and the write operation raises an exception, the serialized JSON string object is not decremented, leaking memory. Each failed write operation leaks the full size of the serialized payload. This vulnerability is fixed in 5.12.1.
Affected products
ultrajson_project: ultrajson
References4
- github.com/ultrajson/ultrajson/security/advisories/GHSA-c38f-wx… ExploitMitigationPatchVendor Advisory
- github.com/ultrajson/ultrajson/security/advisories/GHSA-c38f-wx… ExploitMitigationPatchVendor Advisory
- github.com/ultrajson/ultrajson/commit/82af1d0ac01d09aa40c887b46… Patch
- github.com/ultrajson/ultrajson/releases/tag/5.12.1 ProductRelease Notes
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS 4.0
-
8.7
HIGH
Score source: CNA
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 37 · as of 15 November 2026
- CWE
- CWE-401
Could this be exploited in your environment?
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