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CVE-2026-48104 is an uninitialized memory use vulnerability in the SquashFS archive handler of 7-Zip. It affects versions 9.18 through 26.00. The flaw arises because the handler allocates the internal _blockToNode index array with capacity for every metadata block, but only initializes entries when an inode crosses a block boundary. As a result, a crafted SquashFS image with relatively few inodes spanning many metadata blocks can leave much of the array containing stale heap data. During archive opening, OpenDir uses an attacker-influenced blockIndex derived from the RootInode superblock field to read uninitialized _blockToNode entries and use them as left and right bounds for a binary search over _nodesPos. That search dereferences the midpoint without adequate bounds validation, and if the searched value matches, the resulting index is then used to read a node structure from _nodes and continue directory parsing. This creates a heap-layout-dependent chain of uninitialized read and out-of-bounds read conditions during Open() when a crafted SquashFS archive is opened. The SquashFS handler is enabled by default in stock 7z.dll.
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