Use-after-free in "unicode_escape" decoder with error handler
Summary
| CVE | CVE-2025-4516 |
|---|---|
| State | PUBLISHED |
| Assigner | PSF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2025-05-15 14:15:31 UTC |
| Updated | 2026-07-31 14:16:44 UTC |
| Description | There is an issue in CPython when using `bytes.decode("unicode_escape", error="ignore|replace")`. If you are not using the "unicode_escape" encoding or an error handler your usage is not affected. To work-around this issue you may stop using the error= handler and instead wrap the bytes.decode() call in a try-except catching the DecodeError. |
Risk And Classification
Primary CVSS: v4.0 5.9 MEDIUM from [email protected]
CVSS:4.0/AV:L/AC:H/AT:P/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: 0.001770000 probability, percentile 0.075110000 (date 2026-08-03)
Problem Types: CWE-416 | CWE-416 CWE-416 Use After Free
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 5.9 | MEDIUM | CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/C... |
| 4.0 | CNA | CVSS | 5.9 | MEDIUM | CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
CVSS v4.0 Breakdown
Attack Vector
LocalAttack Complexity
HighAttack Requirements
PresentPrivileges Required
NoneUser Interaction
NoneConfidentiality
NoneIntegrity
NoneAvailability
HighSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS:4.0/AV:L/AC:H/AT:P/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
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Python Software Foundation | CPython | affected 3.9.23 python | Not specified |
| CNA | Python Software Foundation | CPython | affected 3.10.0 3.10.18 python | Not specified |
| CNA | Python Software Foundation | CPython | affected 3.11.0 3.11.13 python | Not specified |
| CNA | Python Software Foundation | CPython | affected 3.12.0 3.12.11 python | Not specified |
| CNA | Python Software Foundation | CPython | affected 3.13.0 3.13.4 python | Not specified |
| CNA | Python Software Foundation | CPython | affected 3.14.0a1 3.14.0b2 python | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/python/cpython/commit/69b4387f78f413e8c47572a85b3478c47eba8142 | [email protected] | github.com | |
| www.openwall.com/lists/oss-security/2025/05/19/1 | af854a3a-2127-422b-91ae-364da2661108 | www.openwall.com | |
| github.com/python/cpython/commit/8d35fd1b34935221aff23a1ab69a429dd156be77 | [email protected] | github.com | |
| mail.python.org/archives/list/[email protected]/thread/L75IPBBTSCY... | [email protected] | mail.python.org | |
| github.com/python/cpython/commit/4398b788ffc1f954a2c552da285477d42a571292 | [email protected] | github.com | |
| github.com/python/cpython/commit/73b3040f592436385007918887b7e2132aa8431f | [email protected] | github.com | |
| www.openwall.com/lists/oss-security/2025/05/16/4 | af854a3a-2127-422b-91ae-364da2661108 | www.openwall.com | |
| github.com/python/cpython/commit/ab9893c40609935e0d40a6d2a7307ea51aec598b | [email protected] | github.com | |
| github.com/python/cpython/pull/129648 | [email protected] | github.com | |
| github.com/python/cpython/commit/6279eb8c076d89d3739a6edb393e43c7929b429d | [email protected] | github.com | |
| github.com/python/cpython/commit/9f69a58623bd01349a18ba0c7a9cb1dad6a51e8e | [email protected] | github.com | |
| github.com/python/cpython/issues/133767 | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.