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CVE-2026-64074
fs/statmount: fix slab out-of-bounds write in statmount_mnt_idmap
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem fs. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64074 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
statmount_mnt_idmap() writes one mapping with seq_printf() and then manually advances seq->count to include the NUL separator. If seq_printf() overflows, seq_set_overflow() sets seq->count to seq->size. The manual seq->count++ changes this to seq->size + 1. seq_has_overflowed() then no longer detects the overflow. The corrupted count returns to statmount_string(), which later executes: seq->buf[seq->count++] = '\0'; This causes a 1-byte NULL out-of-bounds write on the dynamically allocated seq buffer. Fix this by checking for overflow immediately after seq_printf().
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/mnt_idmapping.c
- What this is
- FILESYSTEMS [IDMAPPED MOUNTS]MAINTAINERS section matched on fs/mnt_idmapping.c · linux-fsdevel@vger.kernel.org · Maintained
Show whether Debian builds this, per release
Debian builds this code. Every release with an answer below compiles the affected file into the kernels it ships. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sidy
- ?
- not established - no Makefile entry for the affected file
- y
- built into the kernel image on every flavour - only a patch removes it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS Debian linux-config packages
Signals
- Published
- 2026-07-19 (3 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.15 | 6.18.34 | e37ea2c6f17f |
| 6.15 | 7.0.11 | 93614949dc86 |
| 6.15 | 7.1 | a3bf0f28d4ba |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is reachable only through the statmount(2) syscall when requesting mount UID/GID map strings; there is no network, adjacent, or physical entry path to this code.
- AC:LAttack complexity, low
- An attacker fully controls statmount mask, buffer sizing, mount paths/options, and idmap extent values to reliably drive seq_printf() to overflow at the vulnerable count++ site without depending on uncontrollable timing or layout.
- PR:LPrivileges required, low
- Exploitation requires creating or querying an idmapped mount via statmount, which an unprivileged local user can do in their own user/mount namespaces where CAP_SYS_ADMIN is granted by user namespaces.
- UI:NUser interaction, none
- Triggering the flaw requires only the attacker's own statmount syscall and crafted namespace/mount setup; no action by another user or victim is needed.
- S:UScope, unchanged
- Impact is kernel heap corruption and potential privilege escalation within the same kernel security domain, not a cross-boundary escape such as VM guest-to-host.
- C:HConfidentiality impact, high
- The flaw is a slab out-of-bounds write that corrupts adjacent heap memory; per kernel CVSS guidance, exploitable memory corruption warrants High confidentiality impact even if direct read is not guaranteed.
- I:HIntegrity impact, high
- A one-byte out-of-bounds NULL write into adjacent kmalloc slab objects can corrupt kernel metadata and be leveraged for arbitrary memory modification or code execution.
- A:HAvailability impact, high
- Heap corruption from the out-of-bounds write can cause kernel oops/panic or destabilize the system, and memory-corruption bugs are scored as High availability impact.