rootpwn

high · CVSS v3 7.1

CVE-2026-93203

A race condition in the batman-adv kernel module can corrupt the CRC used to validate claim frames, leading to incorrect routing information

Overview

A race condition in the batman-adv kernel module can corrupt the CRC used to validate claim frames, leading to incorrect routing information in mesh networks. The flaw may cause routing tables to become inconsistent, potentially disrupting network connectivity.

Description

In the Linux kernel, the following vulnerability has been resolved: batman-adv: bla: avoid CRC corruption due to parallel claim add batadv_bla_add_claim() is used to add claims and modify the backbone of claims for CLAIM frames from remote backbones and local packets. When it handles a claim, it needs to either * add the new claim's CRC to the backbone CRC * remove the already existing claim's CRC from the old backbone and add it to the new backbone But when the "new" claim code was running in parallel to the "change backbone" code, it can happen that the CRC was invalid because the backbone_gw of the claim was changed twice in the "new" claim code path: * CPU0 creates the claim for gateway A and publishes it in the claim hash. The crc16 of the address has not yet been added to A's crc at this point. * CPU1 processes a claim frame of gateway B for the same client, finds the just published claim, and performs the ownership change: it switches the pointer to B, removes the crc16 from A's crc - which never contained it - and adds it to B's crc. * CPU0 continues behind the creation branch, unconditionally switches the pointer back to A without compensating B's crc (its remove_crc is false for the creation path), and finally adds the crc16 to A's crc The CRC is then wrong for both: * claim belongs to A: but CRC is not part of backbone A's CRC * claim doesn't belong to B: CRC is still part of backbone B's CRC This wrong CRC is never recomputated from the stored claims. For local backbone claims, this can also not recovered using syncs. To avoid this, split the functionality in clear separate parts: * new claim which always adds claim CRC to the backbone CRC (but never changes the already set backbone_gw of the claim back) * update of existing claim which automatically changes the backbone_gw entry and only updates both backbone CRCs when there was an actual change

Impact

Integrity and availability of mesh routing data are compromised. Incorrect CRCs can cause misrouting or loss of connectivity for devices relying on batman-adv, potentially leading to denial‑of‑service conditions within the affected network.

Remediation

['Upgrade the Linux kernel or batman-adv module to the latest patched release that contains the CRC‑correction fix.', 'If an immediate kernel upgrade is not possible, disable batman-adv on affected nodes or replace it with an alternative routing solution.', 'Verify that the patched module is loaded and that no legacy batman-adv binaries remain.', 'Monitor routing tables and logs for unexpected changes or errors that could indicate residual CRC inconsistencies.']

Risk context

The vulnerability is rated high (CVSS 7.1) with no EPSS data available. Prompt patching is recommended to prevent integrity and availability issues in mesh networks.

Affected products

  • Linux kernel (batman-adv)
  • Ubuntu
  • Debian
  • CentOS
  • Red Hat Enterprise Linux
  • Fedora
  • SUSE Linux Enterprise
  • OpenWrt

Scores

Severity
high
CVSS v2
2.1
CVSS v3
7.1
CVSS v4
—
EPSS
—

batman-adv kernel CRC routing mesh integrity high severity patch

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