UBUNTU-CVE-2026-64533: High severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: fs/ntfs3: validate lcnsfollow in logreplay conversion logreplay() converts DIRPAGEENTRY32 records into DIRPAGEENTRY records when replaying version 0 restart tables. During this conversion, the memmove() length is derived directly from the on-disk lcnsfollow field: memmove(&dp->vcn, &dp0->vcnlow, 2 sizeof(u64) + le32tocpu(dp->lcnsfollow) sizeof(u64)); checkrstbl() validates restart table structure, but does not constrain per-entry lcnsfollow values relative to the entry size. A malformed filesystem image can provide an oversized lcnsfollow value, causing the conversion memmove() to access memory beyond the bounds of the allocated restart table buffer. The same field is later used to bound iteration over pagelcns[], so validating lcnsfollow during conversion also prevents downstream out-of-bounds access from the same malformed metadata. Compute the maximum valid lcnsfollow from the already-validated restart table entry size and reject entries that exceed this bound. Reuse the existing t16/t32 scratch variables already declared in logreplay() to avoid introducing new declarations. [almaz.alexandrovich@paragon-software.com: fixed the conflicts]
Affected Software
Remediation
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-38.38 - Upgrade
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ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
In Linux kernel fs/ntfs3 log_replay() conversion of version 0 restart-table DIR_PAGE_ENTRY_32 records, compute the maximum valid lcns_follow from the already-validated restart-table entry size and reject entries whose lcns_follow exceeds that bound before calling memmove(); reuse the existing t16/t32 scratch variables.
Event History
Frequently Asked Questions
What does an attacker need to exploit this issue?
An attacker needs to cause a system to process a malformed NTFS filesystem image containing a version 0 restart table with an oversized lcns_follow value. The attack is local, requires no privileges, and requires user interaction.
What can happen if a vulnerable system processes the crafted metadata?
The kernel can access memory beyond the allocated restart-table buffer during log replay conversion. The same malformed field can also lead to downstream out-of-bounds access while iterating over page_lcns entries.