Buffer overflow in 7-Zip
CVE-2026-48095
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.
Vulnerability class: Integer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.011 (66.3th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 66th percentile — 66.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.011 · change: +0.005
Affected products
- 7-Zip
- Mcmilk 7-Zip — versions <= 26.00
Weakness classification (CWE)
Public proof-of-concept exploits
References
- https://securitylab.github.com/advisories/GHSL-2026-140_7-Zip/ (Exploit, Third Party Advisory)
- https://sourceforge.net/p/sevenzip/discussion/45797/thread/555e132ba4 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-48095?
- CVE-2026-48095 is a high-severity vulnerability in 7-Zip, classified under Integer Overflow or Wraparound. CVSS score: 8.8/10. Published 2026-06-05.
- How severe is CVE-2026-48095?
- High severity. CVSS v3 base score is 8.8 out of 10.
- Is CVE-2026-48095 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.