CVE-2026-64537 bridge: cfm: reject invalid CCM interval at configuration time
A local attacker with high privileges can cause a kernel denial of service by configuring an invalid CCM interval in the Linux bridge module.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-64537?
CVE-2026-64537 is a denial of service vulnerability in Linux, published on 27 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
bridge: cfm: reject invalid CCM interval at configuration time
ccm_tx_work_expired() re-arms itself via queue_delayed_work() using the configured exp_interval converted by interval_to_us(). When exp_interval is BR_CFM_CCM_INTERVAL_NONE or out of range, interval_to_us() returns 0, causing the worker to fire immediately in a tight loop that allocates skbs until OOM.
Fix this by validating exp_interval at configuration time:
- Constrain IFLA_BRIDGE_CFM_CC_CONFIG_EXP_INTERVAL to the valid range [BR_CFM_CCM_INTERVAL_3_3_MS, BR_CFM_CCM_INTERVAL_10_MIN] in the netlink policy so userspace cannot set an invalid value.
- Reject starting CCM TX in br_cfm_cc_ccm_tx() when exp_interval has not yet been configured (defaults to 0 from kzalloc).
Which versions are affected by CVE-2026-64537?
How do I fix CVE-2026-64537?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-64537 being exploited?
There is no known exploitation of CVE-2026-64537 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-64537, DEBIAN-CVE-2026-64537, GHSA-3frj-6745-gjx4, UBUNTU-CVE-2026-64537.