Executive brief
7-Zip is a widely used file archiving utility. A vulnerability in how it handles NTFS disk images allows an attacker to execute malicious code or crash the application when a user opens or tests a specially crafted file. Because 7-Zip automatically identifies file types by their content, this attack can be triggered even if the malicious file is renamed to look like a standard .zip or .7z archive.
Technical details
A heap buffer overflow exists in the NTFS archive handler of 7-Zip (7z.dll). The root cause is an undefined behavior (UB) during a 32-bit left-shift operation in CInStream::GetCuSize(), where a crafted NTFS image with specific ClusterSizeLog and CompressionUnit values results in a 1-byte allocation for _inBuf. Subsequent calls to ReadStream_FALSE write up to 256 MB of attacker-controlled data into this 1-byte buffer. This leads to a vtable hijack of the CInStream object, which is located near the buffer on the heap. The vulnerability is reachable regardless of file extension due to 7-Zip's signature-based fallback mechanism. Fixed in version 26.01.
Affected products
- Igor Pavlov 7-Zip 26.00 and prior
Timeline
- 2026-04-24: disclosed: Reported to vendor via SourceForge private issue.
- 2026-04-27: patched: Version 26.01 released with fix.
- 2026-06-05: advisory: CVE-2026-48095 published.