UBUNTU-CVE-2026-72193: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: ntfs3: cap RESTARTTABLE free-chain walker at rt->used A crafted NTFS3 disk image triggers an in-kernel infinite loop at mount time, hanging the mounting thread and firing the soft-lockup watchdog within ~22s on multi-CPU hosts (panic with kernel.softlockuppanic=1). The bug is reachable from desktop USB auto-mount on distributions where udisks2 routes the NTFS signature to the in-tree ntfs3 driver (Arch family and an increasing fraction of Fedora / openSUSE / RHEL deployments); CAPSYSADMIN-class manual mount elsewhere. checkrstbl()'s second walker iterates the free-entry singly-linked list headed by rt->firstfree with no upper bound on iteration count: for (off = ff; off;) { if (off == RESTARTENTRYALLOCATED) return false; off = le32tocpu((le32 )Add2Ptr(rt, off)); if (off > ts - sizeof(le32)) return false; } The existing guards cover three exits: end-of-list (off == 0), the in-use marker (off == RESTARTENTRYALLOCATED), and out-of-bounds (off > ts - sizeof(le32)). None of the three prevents an in-bounds cycle. A crafted on-disk RESTARTTABLE whose free chain contains a self-loop or A->B->A cycle whose offsets satisfy: - in range [sizeof(struct RESTARTTABLE), ts - sizeof(le32)] - (off - sizeof(struct RESTARTTABLE)) % rsize == 0 passes all existing guards and spins the mount-time thread forever. Reproduced in UML by hand-forging a 2 MB NTFS3 image whose journal RESTARTTABLE firstfree = 0x18 and whose entry at offset 0x18 stores 0x18 as its next pointer; mount of the forged image with the in-tree ntfs3 driver never returns. Bound the walker by rt->used. Each entry on a legitimate free chain is unique, and the total slot count is ne = le16tocpu (rt->used). A traversal that visits more than ne slots is by construction malformed; reject it as a corrupt RESTARTTABLE. After this patch, mount of the forged image returns with -EINVAL and a logreplay failure message, and mkntfs-produced legitimate images mount cleanly (verified in the same UML harness).
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1117.124~20.04.1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1071.79+fips1 - Upgrade
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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-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - 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-azure-fdeto a version that resolves this vulnerability.Fixed in 7.0.0-1016.16 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
Bound the ntfs3 RESTART_TABLE free-chain walker by rt->used (the total slot count ne); reject the RESTART_TABLE as corrupt if traversal visits more than ne slots.
Event History
Frequently Asked Questions
When can this be triggered without manual mount privileges?
It is reachable through desktop USB auto-mount where udisks2 routes NTFS media to the in-tree ntfs3 driver. The description identifies Arch-family systems and an increasing fraction of Fedora, openSUSE, and RHEL deployments as examples of this routing behavior.
What does an attacker need to provide?
An attacker needs a crafted NTFS3 disk image containing a RESTART_TABLE free-entry chain with an in-bounds cycle, such as a self-loop or an A-to-B-to-A loop. In environments without the relevant auto-mount path, mounting the image manually requires CAP_SYS_ADMIN-class privileges.
What is the operational impact if the vulnerable path is reached?
Mounting the crafted image can place the kernel in an infinite loop, hang the mounting thread, and trigger the soft-lockup watchdog in roughly 22 seconds on multi-CPU hosts. Systems configured with kernel.softlockup_panic=1 may panic.