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CVE-2026-72389
bridge: stp: Fix a potential use-after-free when deleting a bridge
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/bridge. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-72389 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The three STP timers are not supposed to be armed while the bridge is administratively down. They are synchronously deactivated when the bridge is put administratively down and the various call sites check for 'IFF_UP' before arming them. This check is missing from br_topology_change_detection() and it is possible to engineer a situation in which the topology change timer is armed while the bridge is administratively down, resulting in a use-after-free [1] when the bridge is deleted. Fix by adding the missing check and for good measures synchronously shutdown the three timers when the bridge is deleted. [1] ODEBUG: free active (active state 0) object: ffff88811662b9b0 object type: timer_list hint: br_topology_change_timer_expired (net/bridge/br_stp_timer.c:120) WARNING: lib/debugobjects.c:629 at debug_print_object+0x1bc/0x450, CPU#9: ip/359
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/bridge/br_if.c
net/bridge/br_stp.c
- What this is
- ETHERNET BRIDGEMAINTAINERS section matched on net/bridge/ · bridge@lists.linux.dev · Maintained
- Kernel module
- bridge
Check it on the machine
grep -w CONFIG_BRIDGE /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 bridgePrints 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, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_BRIDGE
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
- 7.8 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
- 0.16%, higher than 5.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/bridge
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 | 5.15.212 | c86579b0a2d2 |
| 2.6.12 | 6.1.178 | 297a747f59bf |
| 2.6.12 | 6.6.145 | 4c40eec06eea |
| 2.6.12 | 6.12.97 | 39283907a25e |
| 2.6.12 | 6.18.40 | b4b3458ef88d |
| 2.6.12 | 7.1.5 | 40cbfa3a28e0 |
| 2.6.12 | 7.2 | 2a00517db8de |
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 is via local RTNETLINK/ioctl to create a down bridge, enable kernel STP, enslave ports, and delete the bridge; remote STP BPDU handling is blocked when IFF_UP is clear, so the arming path that leaves timers active on a down bridge is local.
- AC:LAttack complexity, low
- The public PoC uses a reliable, attacker-controlled netlink sequence (down bridge + kernel STP + port state progression + dellink) without winning races; per-port forward-delay timers deterministically reach br_topology_change_detection and arm topology_change_timer before deletion.
- PR:LPrivileges required, low
- All reachable paths (RTM_NEWLINK/DELLINK, IFLA_BR_STP_STATE, enslaving ports) require CAP_NET_ADMIN, which unprivileged users can obtain in user/network namespaces (unshare -Urn, Kubernetes NET_ADMIN, LXC/libvirt network namespaces).
- UI:NUser interaction, none
- Triggering requires only programmatic bridge configuration by the attacker; no victim must click, mount, or open anything beyond the attacker's own netlink operations.
- S:UScope, unchanged
- Impact is kernel memory corruption and privilege escalation within the same kernel/host security domain; it does not cross a VM, container-to-host, or IOMMU boundary by itself.
- C:HConfidentiality impact, high
- Use-after-free of the net_device/net_bridge kmalloc object lets an attacker reclaim freed slab memory and obtain arbitrary kernel read/disclosure primitives from corrupted timer and bridge structures.
- I:HIntegrity impact, high
- Disclosed analysis and PoC show the dangling timer callback can hijack control flow by reclaiming the freed object with attacker-controlled data, replacing the timer function pointer for arbitrary kernel code execution.
- A:HAvailability impact, high
- Deleting the bridge with active STP timers queued causes the per-CPU timer wheel to invoke callbacks on freed memory, producing kernel BUG/oops/panics and denial of service even if full exploitation is not attempted.