Look up another CVE · open CVE-2026-74485 in the interactive tracker
CVE-2026-74485
binfmt_misc: reject a flag character as the field delimiter
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem fs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74485 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The registration string starts with a user chosen delimiter that separates the individual fields. So that the field parsers terminate even on a truncated string create_entry() pads the buffer with that same delimiter: memset(buf + count, del, 8); Most fields are scanned for the delimiter with strchr()/scanarg() and happily stop on the padding. The flags field is different: instead of scanning for the delimiter check_special_flags() consumes the flag characters 'P', 'O', 'C' and 'F' and stops at the first byte that is none of them, relying on the trailing delimiter to end the scan. If the delimiter is itself a flag character the padding no longer acts as a terminator. The scan swallows all eight padding bytes and keeps reading past the end of the allocation until it hits a byte that is not a flag character. For example registering PaPEPPxPPiP with 'P' as the delimiter (name "a", type extension, magic "x", interpreter "i", empty flags) leaves the flag scan running off the end of the buffer. The registration is rejected in the end because the parser does not stop exactly at buf + count, but only after the out of bounds read has already happened. With an unlucky allocation layout the scan can walk into an unmapped page; under KASAN it is reported as a slab out of bounds read. binfmt_misc mounts are available to unprivileged users in a user namespace so the read is reachable without privileges. Reject a delimiter that is one of the flag characters up front. Such a registration was always rejected anyway, only after the out of bounds read, so no valid registration string changes meaning.
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/binfmt_misc.c
- What this is
- EXEC & BINFMT API, ELFMAINTAINERS section matched on fs/*binfmt_*.c · linux-mm@kvack.org · Supported
- Kernel module
- binfmt_misc
Check it on the machine
grep -w CONFIG_BINFMT_MISC /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w binfmt_miscPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_BINFMT_MISC
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 kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.12 | 5.10.265 | 96bd5d4fea29 |
| 2.6.12 | 5.15.216 | 9970e094e5d6 |
| 2.6.12 | 6.1.183 | b29e3c1f375c |
| 2.6.12 | 6.6.151 | 1819f82dee76 |
| 2.6.12 | 6.12.103 | 1853e95c9bfe |
| 2.6.12 | 6.18.44 | 840bb9c49c3e |
| 2.6.12 | 7.1.8 | 9a2d87db3898 |
| 2.6.12 | 7.2 | 8e85d50ba111 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | tracker |
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
- Exploitation requires a local write() to binfmt_misc/register via bm_register_write()->create_entry(); the path is a VFS syscall on a mounted filesystem, not any network protocol or remote packet handler.
- AC:LAttack complexity, low
- An attacker fully controls the registration string and can deterministically choose delimiter P/O/C/F with empty flags so check_special_flags() consumes padding and reads past the kmalloc buffer on every attempt; no race or victim-specific state is required.
- PR:LPrivileges required, low
- binfmt_misc has FS_USERNS_MOUNT; an unprivileged local user can unshare a user namespace, mount binfmt_misc, and write register without init-namespace root, matching the fix commit's stated unprivileged reachability.
- UI:NUser interaction, none
- Triggering is entirely attacker-driven through mounting binfmt_misc and writing a crafted registration string; no victim must open files, click links, or perform any interactive action beyond the attacker's own syscalls.
- S:UScope, unchanged
- The slab out-of-bounds read and any disclosed kernel data remain within the host kernel security authority; this is standard local kernel memory access, not a VM escape, IOMMU bypass, or sandbox boundary crossing.
- C:HConfidentiality impact, high
- check_special_flags() scans past buf+count+8 through adjacent kmalloc/slab memory until a non-P/O/C/F byte, a classic out-of-bounds read that can disclose kernel pointers and other sensitive heap contents for KASLR defeat.
- I:NIntegrity impact, none
- The defect is read-only: check_special_flags() only dereferences bytes beyond the allocation and sets flags on the soon-freed Node; it performs no out-of-bounds write, metadata corruption, or control-flow hijack primitive.
- A:HAvailability impact, high
- The unbounded flag scan can walk into an unmapped page and fault the kernel; KASAN reports slab-out-of-bounds, and the single write() to register is trivially repeatable for denial-of-service.