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CVE-2026-52919
batman-adv: fix tp_meter counter underflow during shutdown
Published 2026-06-24 (4 months ago) by the Linux kernel CNA. Subsystem net/batman-adv. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-52919 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-4665-1 · 2026-07-03 · text | 6.1.176-1 | Update the kernel and reboot. DLA-4665-1 shipped the fix on 2026-07-03, in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| 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
batadv_tp_sender_shutdown() unconditionally decrements the "sending" atomic counter. If multiple paths (e.g. timeout, user cancel, and normal finish) call this function, the counter can underflow to -1. Since the sender logic treats any non-zero value as "still sending", a negative value causes the sender kthread to loop indefinitely. This leads to a use-after-free when the interface is removed while the zombie thread is still active. Fix this by using atomic_xchg() to ensure the counter only transitions from 1 to 0 once. [sven: added missing change in batadv_tp_send]
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/batman-adv/tp_meter.c
- What this is
- BATMAN ADVANCEDMAINTAINERS section matched on net/batman-adv/ · b.a.t.m.a.n@lists.open-mesh.org · Maintained
- Kernel module
- batman_adv
Check it on the machine
grep -w CONFIG_BATMAN_ADV /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 batman_advPrints 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.
- bookworm, trixie, forky, sidMnot 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_BATMAN_ADV
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
- 2026-06-24 (4 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
- 0.12%, higher than 1.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/batman-adv
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.8 | 5.10.258 | e75e2ab463b5 |
| 4.8 | 5.15.209 | abae88fa254f |
| 4.8 | 6.1.175 | c66d20a3ff09 |
| 4.8 | 6.6.142 | c1bac194733a |
| 4.8 | 6.12.92 | 01cefc592388 |
| 4.8 | 6.18.34 | 90ae3eae06b7 |
| 4.8 | 7.0.11 | aeae11c5dad9 |
| 4.8 | 7.1 | 94f3b133168d |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4671-1 | 2026-07-05 | bullseye 6.1.176-1~deb11u1 | tracker |
| DLA-4665-1 | 2026-07-03 | bookworm 6.1.176-1 | tracker |
| DLA-4664-1 | 2026-07-03 | bullseye 5.10.259-1 | 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 vulnerable sender shutdown path is reached through the batman-adv generic netlink tp_meter start/cancel operations and mesh-interface teardown, which are local kernel control interfaces rather than packets alone. Adjacent mesh packets can influence timing, but an attacker must be able to initiate or cancel the tp_meter session locally to reliably hit the underflow.
- AC:LAttack complexity, low
- The underflow occurs when multiple attacker-controllable stop paths act on the same session, such as a short test/timeout plus cancel or teardown. Although timing is involved, the attacker controls the session lifetime and can repeat the race, so this is low complexity.
- PR:LPrivileges required, low
- The tp_meter genl commands use GENL_UNS_ADMIN_PERM, requiring CAP_NET_ADMIN in the caller's user namespace. Because batman-adv is netns-aware and can be driven from user namespaces when available, this is low rather than high privilege.
- UI:NUser interaction, none
- A local attacker with the required namespace capability can create/start/cancel/tear down the tp_meter session without any separate victim action. No user needs to open a file, mount anything, or interact with attacker-controlled data.
- S:UScope, unchanged
- The bug corrupts/uses kernel networking subsystem state within the same kernel security authority. It is not a VM escape, IOMMU bypass, or cross-authority boundary violation.
- C:HConfidentiality impact, high
- The fix commit states the negative sender counter leaves a zombie kthread active and leads to a use-after-free during interface removal. Per kernel scoring guidance, a kernel UAF is treated as potentially enabling high confidentiality impact.
- I:HIntegrity impact, high
- The resulting use-after-free is kernel memory corruption and can plausibly be shaped into write/control-flow primitives in the most severe reasonable scenario. Per guidance, kernel UAFs are scored as high integrity impact.
- A:HAvailability impact, high
- At minimum, the negative counter can keep the sender kthread looping indefinitely and hang teardown; the documented UAF can also crash the kernel. This is high availability impact.