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CVE-2026-74689
net/atm: fix slab-out-of-bounds read in vcc_setsockopt()
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem net/atm. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74689 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 | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. 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
vcc_setsockopt() contained an ineffective optlen check: if (__SO_LEVEL_MATCH(optname, level) && optlen != __SO_SIZE(optname)) return -EINVAL; If __SO_LEVEL_MATCH(optname, level) evaluated to false (e.g. if the caller passed a mismatched level), the length check optlen != __SO_SIZE(optname) was short-circuited and bypassed. Execution then fell through to switch(optname), calling copy_from_sockptr() assuming optval contained sufficient space. Furthermore, even if level matched, a cgroup BPF setsockopt filter could shrink optlen after entry. Because copy_from_sockptr() on kernel pointers uses memcpy(), this leads to a KASAN slab-out-of-bounds read when optlen is smaller than the expected structure size. Fix this by using copy_safe_from_sockptr(), which unconditionally validates that optlen is at least the expected size before copying. Also change the local 'value' variable type from 'unsigned long' to 'int' so that SO_SETCLP matches its sizeof(int) ABI encoding on 64-bit systems.
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.
net/atm/common.c
- What this is
- ATMMAINTAINERS section matched on net/atm/ · linux-atm-general@lists.sourceforge.net · Maintained
- Kernel module
- atm
Check it on the machine
grep -w CONFIG_ATM /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 atmPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_ATM
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
- 2026-08-22 (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
- 0.14%, higher than 2.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/atm
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 | 6.1.183 | b3bcd5d65ac0 |
| 2.6.12 | 6.6.152 | 35f258fee9ed |
| 2.6.12 | 6.12.104 | 6eb6af887109 |
| 2.6.12 | 6.18.45 | 9f77c1ab3821 |
| 2.6.12 | 7.1.9 | 2c5988c7349c |
| 2.6.12 | 7.2 | d0c80dbb9704 |
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
- The bug is reached only via the local setsockopt(2) syscall on an AF_ATMPVC/AF_ATMSVC socket (do_sock_setsockopt -> pvc_setsockopt/svc_setsockopt -> vcc_setsockopt); no remote ATM packet or network-facing handler invokes this path.
- AC:LAttack complexity, low
- The attacker fully controls level, optname, and optlen; passing a mismatched level bypasses the short-circuited length check, and cgroup BPF setsockopt can shrink optlen after entry, deterministically triggering a full-size memcpy past a small kmalloc buffer with no race.
- PR:LPrivileges required, low
- No capability check guards SO_ATMQOS or SO_SETCLP on unconnected ATM sockets; any unprivileged local user in init_net (required because ATM socket creation rejects non-init network namespaces) can open AF_ATMPVC sockets and issue the crafted setsockopt without CAP_NET_ADMIN.
- UI:NUser interaction, none
- The attacker triggers the out-of-bounds read entirely from their own process with a single crafted setsockopt call; no victim interaction or cooperation is required.
- S:UScope, unchanged
- Impact is kernel heap memory disclosure and potential crash within the host kernel security boundary; no VM escape, IOMMU bypass, or cross-sandbox boundary crossing occurs.
- C:HConfidentiality impact, high
- copy_from_sockptr() performs a slab-out-of-bounds read of up to 92 bytes (struct atm_qos) or 8 bytes (SO_SETCLP) past a kmalloc buffer into kernel stack memory; adjacent slab contents can populate vcc->qos and be retrieved via subsequent SO_ATMQOS getsockopt.
- I:NIntegrity impact, none
- The defect is a pure out-of-bounds read with no arbitrary kernel write, heap corruption, or control-flow hijack primitive; although leaked bytes may influence vcc->qos if validation passes, no attacker-controlled data modification occurs.
- A:HAvailability impact, high
- The KASAN-reported slab-out-of-bounds read triggers kernel oops on hardened kernels, and reading past a small kmalloc object into adjacent slab memory on production kernels risks faulting on unmapped redzone pages or corrupting adjacent objects leading to panic.