CVE-2026-64324: udf: validate free block extents against the partition length

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-25 · updated 2026-10-19
Weakness: CWE-129

Description

In the Linux kernel, the following vulnerability has been resolved: udf: validate free block extents against the partition length udf_free_blocks() checks the logical block number and count against the partition length, but drops the extent offset from that final bound. A crafted extent can pass the guard while logicalBlockNum + offset + count points past the partition, which later indexes past the space bitmap array. A single ftruncate(2) on a file backed by such an extent reliably panics the kernel. This is a local availability issue. On desktop systems where UDisks/polkit allows the active user to mount removable UDF media without CAP_SYS_ADMIN, an unprivileged local user can supply the crafted filesystem and trigger the panic by truncating a writable file on it. Systems that require root or CAP_SYS_ADMIN to mount the image have a higher prerequisite. No confidentiality or integrity impact is claimed: the reproduced primitive is an out-of-bounds read of a bitmap pointer slot followed by a kernel panic. Use the already computed logicalBlockNum + offset + count value for the partition length check. Also make load_block_bitmap() reject an out-of-range block group before indexing s_block_bitmap[], so corrupted callers cannot walk past the flexible array.

Affected products

Linux kernel: from 4.19.320 before 4.20; from 5.4.282 before 5.5; from 5.10.224 before 5.10.261; from 5.15.165 before 5.15.212; from 6.1.105 before 6.1.178; from 6.6.46 before 6.6.145 — fixed in 4.20, 5.10.261, 5.15.212, 5.5, 6.1.178, 6.12.96

How to fix

Upgrade to a fixed version: Linux kernel 4.20, 5.10.261, 5.15.212, 5.5. Check the vendor advisory for mitigations.

References

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