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CVE-2026-52914
batman-adv: fix fragment reassembly length accounting
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-2026-52914 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
batman-adv keeps a running payload length for queued fragments and uses it to validate a fragment chain before reassembly. That accounting currently allows the accumulated fragment length to be truncated during updates. As a result, malformed fragment chains can bypass the intended validation and drive reassembly with inconsistent length state, leading to a local denial of service. Fix the accounting by storing the accumulated length in a length-typed field and rejecting update overflows before the existing validation logic runs. The fix was verified against the original reproducer and against valid fragment reassembly paths.
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/fragmentation.c
net/batman-adv/types.h
- 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
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.51%, higher than 42.4% 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 |
|---|---|---|
| 3.13 | 5.10.258 | e4f3f6b818aa |
| 3.13 | 5.15.209 | 37be61825b15 |
| 3.13 | 6.1.175 | 975563c5de11 |
| 3.13 | 6.6.142 | f653b040dad1 |
| 3.13 | 6.12.92 | e910dbf50912 |
| 3.13 | 6.18.34 | 3eb8bcb82339 |
| 3.13 | 7.0.11 | fdb2c96efb2b |
| 3.13 | 7.1 | 9cd3f16c320b |
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:NAttack vector, network
- The vulnerable path is reached by received ETH_P_BATMAN BATADV_UNICAST_FRAG network frames through batadv_batman_skb_recv(). A remote BATMAN-adv mesh peer can deliver crafted fragments to the target node without using a local syscall or device file.
- AC:LAttack complexity, low
- The attacker controls the fragment sequence number, fragment number, total_size field, and payload lengths needed to trigger the wrapped accounting. In a reasonable high-MTU BATMAN-adv deployment, no race or victim-specific state beyond an active mesh interface is required.
- PR:NPrivileges required, none
- The receive path performs packet-format, destination-MAC, mesh-state, and originator lookups, but no authentication or privilege check on the sender. An attacker sending accepted BATMAN-adv frames needs no privileges on the target.
- UI:NUser interaction, none
- Exploitation is triggered solely by delivery of crafted BATMAN-adv fragments to an active interface. No victim user action is required.
- S:UScope, unchanged
- The vulnerability corrupts or crashes the kernel handling the same BATMAN-adv/networking security authority. It does not cross a separate boundary such as guest-to-host or IOMMU isolation.
- C:HConfidentiality impact, high
- The truncated length state can drive reassembly with inconsistent sizing and attacker-controlled fragment data, creating plausible kernel memory corruption. Under the overestimate rule, such corruption can be leveraged for kernel memory disclosure.
- I:HIntegrity impact, high
- The reassembly path can size the output skb from the wrapped total while copying more attacker-controlled fragment data than accounted. This is defensibly an out-of-bounds write/kernel memory corruption condition.
- A:HAvailability impact, high
- At minimum, the malformed chain can hit skb tail overrun BUG/panic behavior or otherwise corrupt kernel memory. That gives a reliable kernel crash/denial of service.