CVE-2026-6100
HighCVSS 8.1Exploitation Probability (EPSS)
Low risk45th percentile - higher than 45% of all known CVEs
Summary
A use-after-free vulnerability was found in Python's standard library in `lzma.LZMADecompressor`, `bz2.BZ2Decompressor`, and `gzip.GzipFile`. It occurs when a memory allocation fails with a `MemoryError` and the decompressor instance is reused. The fix cleans up the dangling pointer in this specific error condition.
Risk Assessment
The organization may face unpredictable behavior or potential exploitation if a process is under memory pressure and reuses decompressor instances after a `MemoryError`. This could lead to application crashes or other adverse effects.
Recommendation
It is recommended to update Python to a version containing the fix. If an update is not possible, avoid reusing decompressor instances after a `MemoryError` and instead create a new instance for each decompression operation.
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Original NVD description (English source)
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.