CVE-2026-119602: libmspack through 0.11alpha Uninitialized Memory Disclosure via MS-ZIP Decompressor Window

Severity: low (CVSS 3.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-30 · updated 2026-10-30
Weakness: CWE-908

Description

libmspack through 0.11alpha contains an uninitialized memory disclosure vulnerability in the MS-ZIP decompressor that allows attackers to leak heap data via unchecked back-reference distances. Attackers can supply a crafted MS-ZIP CAB file whose first block begins with a back-reference, causing cabd->extract() to write up to 32 KiB of stale heap memory into extracted output.

Affected products

kyz libmspack: through 0.11alpha

References

https://github.com/kyz/libmspack
https://github.com/kyz/libmspack/blob/v0.11alpha/libmspack/mspack/mszipd.c#L264-L276
https://github.com/kyz/libmspack/issues/60
https://hackmd.io/@haindpwn/libmspack-mszip-uninit-window-info-leak
https://www.vulncheck.com/advisories/libmspack-through-0-11alpha-uninitialized-memory-disclosure-via-ms-zip-decompressor-window

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