CVE-2026-48104 GHSL-2026-120: 7-Zip SquashFS BlockToNode uninitialized heap read
Attackers can cause denial of service or disclose heap memory by tricking users into opening a crafted SquashFS archive in 7-Zip.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-48104?
CVE-2026-48104 is a medium-severity vulnerability in mcmilk 7-Zip, published on 5 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
7-Zip is a file archiver with a high compression ratio. Versions 9.18 through 26.00 contain an uninitialized heap read in the SquashFS archive handler caused by a sparsely populated index array. In the SquashFS handler, _blockToNode is allocated with capacity for every metadata block but populated only when an inode crosses a block boundary, so a crafted image with few inodes spanning many blocks leaves most slots holding raw heap contents (the underlying allocator does not zero-initialize POD storage). When OpenDir looks up an attacker-influenced blockIndex (derived from the RootInode superblock field), it reads two of these uninitialized slots and passes them as the left/right bounds of a binary search over _nodesPos, which dereferences the midpoint without bounds checking; if the resulting value happens to match the search key, the returned index is used to read a full node struct from _nodes whose fields feed further directory parsing, forming a chained OOB read primitive that is heap-layout-dependent and not reliably triggerable. The SquashFS handler is enabled by default in stock 7z.dll and the issue triggers during Open() with no interaction beyond opening the file; impact is denial of service from wild-pointer dereference and potential heap information disclosure, with no write primitive. Version 26.01 fixes the issue.
Which versions are affected by CVE-2026-48104?
It affects 1 product.
Products include 7-Zip 7-Zip.
How do I fix CVE-2026-48104?
Upgrade to a fixed version.
Is CVE-2026-48104 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48104 exists.
Other vulnerabilities in mcmilk 7-Zip
Sources
Also known as ALPINE-CVE-2026-48104, DEBIAN-CVE-2026-48104, ECHO-f5e5-f521-ddd7, MINI-p88c-h56p-q7r5, UBUNTU-CVE-2026-48104.