Integer Overflow or Wraparound Affecting 7zip package, versions <26.01-r0


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

Social Trends
EPSS
1.12% (63rd percentile)

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  • Snyk IDSNYK-ALPINE324-7ZIP-17376614
  • published19 Jun 2026
  • disclosed5 Jun 2026

Introduced: 5 Jun 2026

CVE-2026-48095  (opens in a new tab)
CWE-190  (opens in a new tab)
CWE-787  (opens in a new tab)

How to fix?

Upgrade Alpine:3.24 7zip to version 26.01-r0 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream 7zip package and not the 7zip package as distributed by Alpine. See How to fix? for Alpine:3.24 relevant fixed versions and status.

7-Zip is a file archiver with a high compression ratio. Versions 26.00 and prior contain a heap buffer overflow vulnerability caused by an under-allocation in the NTFS compressed stream buffer (GetCuSize shift UB), potentially allowing attackers to cause arbitrary code execution or application crashes. CInStream::GetCuSize() in the NTFS handler computes the compression-unit buffer size as (UInt32)1 << (BlockSizeLog + CompressionUnit), and a crafted image with ClusterSizeLog >= 28 and CompressionUnit == 4 drives the exponent to 32, which is undefined behavior and collapses on x86/x64 so _inBuf is allocated as 1 byte. ReadStream_FALSE then writes up to 256 MB of attacker-controlled data into that 1-byte buffer in 64 KB iterations, and because the CInStream object sits only 304 bytes after _inBuf, its vtable pointer is overwritten and the next dispatched call achieves a vtable hijack. On 32-bit builds the overflow is unconditionally reached; on 64-bit it requires the parallel 8 GB _outBuf allocation to succeed, otherwise failing closed to denial of service. The NTFS handler is enabled by default in stock 7z.dll and, via signature-based fallback matching "NTFS " at offset 3, will open a crafted image regardless of file extension during extraction or testing. Version 26.01 fixes the issue.

CVSS Base Scores

version 3.1