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CVE-2026-80521
af_unix: Unlink scc_entry in unix_del_edge().
Published 2026-08-26 (2 months ago) by the Linux kernel CNA. Subsystem net/unix. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-80521 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-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Kyle Zeng reported that GC could free a dead SCC partially. The scenario is as follows: 1) Create two SCCs: X -. A <-> B ^--' 2) Run the following concurrently: 2-1) send() sk-B to sk-B from sk-X 2-2) close() both A and B At 2-1), there is a small window where unix_add_edges() publishes a new edge (B <-> B) to GC but its skb is not queued by skb_queue_tail(). If 2-2) completes before skb_queue_tail() and GC is triggered, it judges A <-> B as dead, but B is not freed because GC cannot collect the not-yet-queued skb holding the B <-> B edge. X -. A <-> B -. This edge is visible ^--' ^..' but skb is not This itself is not a problem since the next GC run will judge B as dead as well and free it finally. X -. A <.> B -. ^--' ^--' However, X's SCC forces the next GC to call unix_walk_scc_fast(), and it iterates over A through B's scc_entry. Let's unlink scc_entry before freeing the vertex in unix_del_edge().
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/unix/garbage.c
- What this is
- NETWORKING [UNIX SOCKETS]MAINTAINERS section matched on net/unix/ · Maintained
Check it on the machine
grep -w CONFIG_UNIX /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.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_UNIX
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
- 2026-08-26 (2 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 5.9% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/unix
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.1.141 | 6.1.189 | 2b6c2842692d |
| 6.6.93 | 6.6.158 | 6fda5c51b8e4 |
| 6.10 | 6.12.111 | 1293fd69a50d |
| 6.10 | 6.18.53 | fe198b077864 |
| 6.10 | 7.1.10 | e3702470ced9 |
| 6.10 | 7.2 | 594d90519502 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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 only reachable through local AF_UNIX syscalls (socket/sendmsg with SCM_RIGHTS and close) that drive unix_add_edges(), unix_del_edge(), and unix_gc(); AF_UNIX is host-local IPC with no remote packet, Bluetooth, WiFi, or physical bus entry path.
- AC:LAttack complexity, low
- Exploitation requires racing sendmsg() (scm_stat_add/unix_add_edges before skb_queue_tail) against concurrent close() that triggers GC; the attacker controls both threads, can pin CPUs, and can retry until the window is hit, so success does not depend on conditions outside attacker control.
- PR:LPrivileges required, low
- An unprivileged local user can create AF_UNIX sockets, pass socket file descriptors via SCM_RIGHTS to form inflight reference cycles, and close sockets to schedule unix_gc(); no real-root capabilities, special namespaces, or non-default kernel configuration are required.
- UI:NUser interaction, none
- The attacker sets up the cyclic inflight graph, performs the concurrent self-send and close operations, and forces garbage collection from its own processes; no separate victim user action or cooperating peer is needed beyond the attacker's own sockets.
- S:UScope, unchanged
- The use-after-free corrupts kernel heap/list state during AF_UNIX garbage collection within the same kernel security authority; exploitation yields standard local privilege escalation rather than crossing a VM, IOMMU, or inter-tenant sandbox boundary.
- C:HConfidentiality impact, high
- Freed struct unix_vertex objects remain linked through stale scc_entry; unix_walk_scc_fast(), unix_scc_dead(), and unix_collect_skb() dereference freed vertex->edges and predecessor socket receive queues, giving a slab UAF read primitive controllable through heap grooming.
- I:HIntegrity impact, high
- The same UAF enables reclaiming freed vertices and influencing GC list iteration and skb_queue_splice_init() during unix_collect_skb(), providing memory corruption primitives suitable for arbitrary kernel writes, control-flow hijack, and local privilege escalation.
- A:HAvailability impact, high
- Iterating or collecting through a freed vertex reliably triggers kernel oops/panic (KASAN slab-use-after-free), and corrupt GC graph state can crash the host or deny service to local workloads even when full exploitation is not attempted.