CVE-2026-74659 net: bridge: mrp: fix uninitialised bytes on the wire
An attacker on the local network segment can read uninitialized kernel memory from MRP test frames if the bridge MRP feature is enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74659?
CVE-2026-74659 is a vulnerability in Linux, published on 22 Aug 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:
net: bridge: mrp: fix uninitialised bytes on the wire
br_mrp_alloc_test_skb() builds MRP test frames on an skb from dev_alloc_skb(), which does not clear the linear data area. On the MRA ring-role branch the sub-option TLV header is appended with
sub_tlv = skb_put(skb, sizeof(*sub_tlv)); sub_tlv->type = BR_MRP_SUB_TLV_HEADER_TEST_AUTO_MGR;
so sub_tlv->length is never written, and the two trailing alignment bytes are appended with a bare skb_put() that does not clear them either. The neighbouring oui and sub_opt regions are explicitly zeroed, so three uninitialised bytes are left in every MRA MRP_Test frame that goes out.
Put the sub-option TLV header and the alignment padding in a single skb_put_zero(), which clears both. The AUTO_MGR sub-TLV carries no payload, so the zeroed length field is already the value it should have.
Which versions are affected by CVE-2026-74659?
How do I fix CVE-2026-74659?
Apply the vendor's patch.
Is CVE-2026-74659 being exploited?
There is no known exploitation of CVE-2026-74659 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-74659, DEBIAN-CVE-2026-74659, GHSA-j5v6-9qh5-x594, UBUNTU-CVE-2026-74659.