CVE-2026-6100 | Python CPython up to 3.14.x Decompression Call use after free (ID 148395)

VDB-357209 · CVE-2026-6100 · ID 148395 PYTHON CPYTHON UP TO 3.14.X DECOMPRESSION CALL USE AFTER FREE HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 5.4 $0-$5k 3.07 Summaryinfo A vulnerability classified as critical has been found in Python CPython up to 3.14.x. The affected element is the function lzma.LZMADecompressor/bz2.BZ2Decompressor/gzip.GzipFile of the component Decompression Call Handler. The manipulation leads to use after free. This vulnerability is traded as CVE-2026-6100. It is possible to initiate the attack remotely. There is no exploit available. It is recommended to upgrade the affected component. Detailsinfo A vulnerability was found in Python CPython up to 3.14.x. It has been rated as critical. This issue affects the function lzma.LZMADecompressor/bz2.BZ2Decompressor/gzip.GzipFile of the component Decompression Call Handler. The manipulation with an unknown input leads to a use after free vulnerability. Using CWE to declare the problem leads to CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Impacted is confidentiality, integrity, and availability. The summary by CVE is: Use-after-free (UAF) was possible in the `lzma.LZMADecompressor`, `bz2.BZ2Decompressor`, and `gzip.GzipFile` when a memory allocation fails with a `MemoryError` and the decompression instance is re-used. This scenario can be triggered if the process is under memory pressure. The fix cleans up the dangling pointer in this specific error condition. The vulnerability is only present if the program re-uses decompressor instances across multiple decompression calls even after a `MemoryError` is raised during decompression. Using the helper functions to one-shot decompress data such as `lzma.decompress()`, `bz2.decompress()`, `gzip.decompress()`, and `zlib.decompress()` are not affected as a new decompressor instance is used per call. If the decompressor instance is not re-used after an error condition, this usage is similarly not vulnerable. The weakness was shared by Stan Ulbrych and Ryan Hileman as 148395. The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-6100 since 04/10/2026. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. Upgrading to version 3.15.0 eliminates this vulnerability. Applying the patch 6a5f79c8d7bbf22b083b240910c7a8781a59437d is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version. Productinfo Type Programming Language Software Vendor Python Name CPython Version 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 License open-source Website Product: https://github.com/python/cpython/ CPE 2.3info 🔒 🔒 🔒 CPE 2.2info 🔒 🔒 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CNA CVSS-B Score: 🔒 CNA CVSS-BT Score: 🔒 CNA Vector: 🔒 CVSSv3info VulDB Meta Base Score: 5.6 VulDB Meta Temp Score: 5.4 VulDB Base Score: 5.6 VulDB Temp Score: 5.4 VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Use after free CWE: CWE-416 / CWE-119 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Yes Availability: 🔒 Status: Not defined Price Prediction: 🔍 Current Price Estimation: 🔒 0-Day Unlock Unlock Unlock Unlock Today Unlock Unlock Unlock Unlock Threat Intelligenceinfo Interest: 🔍 Active Actors: 🔍 Active APT Groups: 🔍 Countermeasuresinfo Recommended: Upgrade Status: 🔍 0-Day Time: 🔒 Upgrade: CPython 3.15.0 Patch: 6a5f79c8d7bbf22b083b240910c7a8781a59437d Timelineinfo 04/10/2026 CVE reserved 04/13/2026 +3 days Advisory disclosed 04/13/2026 +0 days VulDB entry created 04/13/2026 +0 days VulDB entry last update Sourcesinfo Product: github.com Advisory: 148395 Researcher: Stan Ulbrych, Ryan Hileman Status: Confirmed CVE: CVE-2026-6100 (🔒) GCVE (CVE): GCVE-0-2026-6100 GCVE (VulDB): GCVE-100-357209 Entryinfo Created: 04/13/2026 21:44 Changes: 04/13/2026 21:44 (73) Complete: 🔍 Cache ID: 99:BC7:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸