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CVE-2026-64089
batman-adv: tt: fix negative last_changeset_len
Published 2026-07-19 (3 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-2026-64089 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 | 6.1.176-1 | Update the kernel and reboot. Fixed 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_piv_tt::last_changeset_len len was declared as s16, but the field is never intended to hold a negative value. When a value greater than 32767 is assigned, it wraps to a negative signed integer. In batadv_send_my_tt_response(), last_changeset_len is temporarily widened to s32. The incorrectly negative s16 value propagates into the s32, causing batadv_tt_prepare_tvlv_local_data() to allocate a full sized buffer but populates only a small portion of it with the collected changeset. All remaining bits are kept uninitialized. Using an u16 avoids this type confusion and ensures that no (negative) sign extension is performed in batadv_send_my_tt_response().
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/types.h
- What this is
- BATMAN ADVANCEDMAINTAINERS section matched on net/batman-adv/ · b.a.t.m.a.n@lists.open-mesh.org · Maintained
Show whether Debian builds this, per release
Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.
- bookworm, trixie, forky, sid?
- ?
- not established - no Makefile entry for the affected file
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
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
Signals
- Published
- 2026-07-19 (3 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
- 0.55%, higher than 44.9% 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 |
|---|---|---|
| 3.1 | 5.10.258 | 6314089acf0d |
| 3.1 | 5.15.209 | 55dc41fe8821 |
| 3.1 | 6.1.175 | c424e8519ac7 |
| 3.1 | 6.6.142 | 22d59c72f4a4 |
| 3.1 | 6.12.92 | eb235472b52e |
| 3.1 | 6.18.34 | 179eb62506a0 |
| 3.1 | 7.0.11 | d29abf70c665 |
| 3.1 | 7.1 | fc92cdfcb295 |
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 bug is reached when a remote mesh peer's TT_REQUEST is processed via batman-adv's network receive path (batadv_recv_unicast_tvlv), which handles ETH_P_BATMAN packets from network-facing mesh interfaces without requiring local access.
- AC:LAttack complexity, low
- Once the victim has a wrapped last_changeset_len (achievable on high-MTU mesh nodes with >2730 TT changes), the attacker reliably triggers the bug by sending a crafted TT_REQUEST with matching ttvn and without BATADV_TT_FULL_TABLE; no race or victim-dependent timing is required.
- PR:NPrivileges required, none
- Exploitation requires only the ability to send batman-adv protocol packets as a mesh peer; no account, credentials, or elevated privileges on the victim system are needed, and TT_REQUEST handling has no authentication gate beyond being a known originator in the mesh.
- UI:NUser interaction, none
- The victim administrator or end user need take no action during exploitation; the attacker sends a TT_REQUEST and the kernel processes it automatically in response to received mesh traffic.
- S:UScope, unchanged
- The vulnerability corrupts kernel heap memory and leaks kernel data within the kernel's own security boundary; it does not cross into another security authority such as a VM guest-to-host or sandbox escape.
- C:HConfidentiality impact, high
- Sign-extended negative last_changeset_len causes memcpy() to read far beyond the small last_changeset buffer (OOB heap read), and the oversized kmalloc response buffer retains uninitialized kernel memory that is copied into the TT_RESPONSE sent back to the attacker.
- I:HIntegrity impact, high
- The same memcpy() with a sign-extended negative length writes far beyond the allocated tt_change region in the kmalloc buffer, causing out-of-bounds heap corruption that can be leveraged for arbitrary kernel writes or control-flow hijacking.
- A:HAvailability impact, high
- The massive out-of-bounds memcpy() from a wrapped s16 length will cause kernel memory corruption, oops, or panic, and even partial execution leaks uninitialized data before potential crash.