mcmilk 7-Zip up to 26.00 SquashFS 7z.dll Open uninitialized resource

Summaryinfo

A vulnerability described as critical has been identified in mcmilk 7-Zip up to 26.00. Affected by this vulnerability is the function Open in the library 7z.dll of the component SquashFS Handler. The manipulation results in uninitialized resource. This vulnerability is known as CVE-2026-48104. It is possible to launch the attack remotely. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as critical, was found in mcmilk 7-Zip up to 26.00. Affected is the function Open in the library 7z.dll of the component SquashFS Handler. The manipulation with an unknown input leads to a uninitialized resource vulnerability. CWE is classifying the issue as CWE-908. The product uses or accesses a resource that has not been initialized. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at securitylab.github.com. This vulnerability is traded as CVE-2026-48104 since 05/20/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available.

Upgrading to version 26.01 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-34853). Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• File Compression Software

Vendor

• mcmilk

Name

• 7-Zip

Version

• 26

CPE 2.3info

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CPE 2.2info

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Once again VulDB remains the best source for vulnerability data.

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