Security readout for executives and security teams
Plain-English summary
A memory safety flaw can crash affected CPython processes when specific malformed bytes are decoded using the "unicode_escape" codec with "ignore" or "replace" error handling. Applications not using that exact combination are not affected. The supplied evidence indicates availability impact, not data theft or modification.
Executive priority
Use targeted, moderate-priority remediation. Quickly identify internet-facing or business-critical services using the affected pattern, then upgrade or apply the documented workaround. Systems without that pattern do not require emergency action for this CVE. Escalate if exposure to untrusted input is confirmed.
Technical view
CVE-2025-4516 is a CWE-416 use-after-free in CPython's "unicode_escape" decoder. The CVSS 4.0 score is 5.9, with local access, high complexity, prerequisite conditions, and high vulnerable-system availability impact. The source bundle lists multiple CPython branches but does not clearly identify fixed release numbers.
Likely exposure
Exposure is narrow: code must decode bytes with "unicode_escape" while specifying errors="ignore" or errors="replace". Risk increases when untrusted or attacker-influenced bytes can reach that path. Inventory results should be confirmed against Python's advisory because the supplied affected-version data is incomplete.
Exploitation context
The supplied CVSS vector describes local attack access, high complexity, and prerequisite conditions. CISA KEV status is false, and no supplied source establishes active exploitation. Treat claims of remote exploitation or code execution as unsubstantiated by this bundle.
Researcher notes
The evidence supports a narrowly triggered use-after-free and denial-of-service risk. The affected list contains ambiguous version entries, including "0" and branch starting points, so it should not be interpreted as precise fixed-release guidance. Review the linked advisory and branch commits before making version-based conclusions.
Mitigation direction
- Upgrade to a vendor-supported CPython release containing the referenced corrections after confirming applicable release guidance.
- As a workaround, remove the error handler and catch the decoding exception around the decode operation.
- Prioritize applications where untrusted bytes reach the affected decoding pattern.
- Retest decoding behavior after changing error handling or upgrading CPython.
Validation and detection
- Search application and dependency code for "unicode_escape" decoding combined with "ignore" or "replace" error handling.
- Record deployed CPython versions and compare them with the Python security advisory and supported fixed releases.
- Trace whether untrusted bytes can reach each identified decoding call.
- Run controlled regression tests covering malformed input, expected exceptions, and process stability.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-416: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2025-4516 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.9 (4.0)
- Known Exploited
- No
- Published
Vector: 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
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
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——PSFVulnerability scoring details
Base CVSS 4.0 score
5.9MediumVector: 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
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/python/cpython/issues/133767CVE reference, PSF · issue-tracking
- https://github.com/python/cpython/pull/129648CVE reference, PSF · patch
- https://mail.python.org/archives/list/security-announce@python.org/thread/L75IPBBTSCYEF56I2M4KIW353BB3AY74/CVE reference, PSF · vendor-advisory
- https://github.com/python/cpython/commit/69b4387f78f413e8c47572a85b3478c47eba8142CVE reference, PSF · patch
- https://github.com/python/cpython/commit/9f69a58623bd01349a18ba0c7a9cb1dad6a51e8eCVE reference, PSF · patch
- https://github.com/python/cpython/commit/4398b788ffc1f954a2c552da285477d42a571292CVE reference, PSF · patch
- https://github.com/python/cpython/commit/6279eb8c076d89d3739a6edb393e43c7929b429dCVE reference, PSF · patch
- https://github.com/python/cpython/commit/73b3040f592436385007918887b7e2132aa8431fCVE reference, PSF · patch
- https://github.com/python/cpython/commit/8d35fd1b34935221aff23a1ab69a429dd156be77CVE reference, PSF · patch
- https://github.com/python/cpython/commit/ab9893c40609935e0d40a6d2a7307ea51aec598bCVE reference, PSF · patch
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.