CVE-2026-64531
EPSS 0.1%Public PoC exists, vendor patching rapidly, but KEV unlisted and EPSS minimal suggests low real-world exploitation yet.
What: Linux kernel Open vSwitch netlink attribute handling flaw allowing oversized nested action attributes to bypass validation, enabling local privilege escalation via malformed CLONE/CT actions (CVSS unavailable; EPSS 0.00161).
Why it matters: Public PoC and patch released within hours of embargo lift; multiple distributions racing to deploy fixes. Local-only attack surface limits immediate remote risk, but kernel privilege escalation bugs warrant urgent triage in multi-tenant environments.
Where it's seen: Security mailing lists and distro advisory channels; vendor patches shipped within 3 hours; social media tracks as trending CVE with PoC labeled "OVSwrap"; defenders already integrating fixes.
RISK: ELEVATED — Local root in widely-deployed kernel subsystem; patch available but adoption lag creates window.
Description
In the Linux kernel, the following vulnerability has been resolved: net: openvswitch: reject oversized nested action attrs Open vSwitch stores generated flow actions as nlattrs, whose nla_len field is u16. Commit a1e64addf3ff ("net: openvswitch: remove misbehaving actions length check") allowed the total sw_flow_actions stream to grow beyond 64 KiB, which is valid, but also removed the last guard preventing a generated nested action attribute from exceeding U16_MAX. An oversized generated container can thus be closed with a truncated nla_len. A later dump or teardown then walks a structurally different stream than the one that was validated. In particular, an oversized nested CLONE/CT action may cause subsequent bytes in the generated stream to be interpreted as independent actions. Keep the larger total-action-stream behavior, but make nested action close reject generated containers that do not fit in nla_len, and return the error through all callers. For recursive SAMPLE, CLONE, DEC_TTL, and CHECK_PKT_LEN builders, trim resource-owning action-list tails in reverse construction order before discarding failed wrappers, so resources copied into the rejected tails are released before the wrappers are removed. Most failed outer wrappers are discarded by truncating actions_len after child resources have been released. CHECK_PKT_LEN also trims its parent after branch resources are gone. SET/TUNNEL close failures unwind their known tun_dst ownership directly, and SET_TO_MASKED has no external ownership and truncates on close failure.
References
- https://git.kernel.org/stable/c/1b41cbe05b184f8861712f0806cc0c4f5d8c6dfe
- https://git.kernel.org/stable/c/3f1f755366687d051174739fb99f7d560202f60b
- https://git.kernel.org/stable/c/ab855641241387db062a5e41d9ad6b8561542572
- https://git.kernel.org/stable/c/c66bd2626c2764f23764ff0f8277f44a9cfe8349
- https://git.kernel.org/stable/c/d573250d228401f707f4dbc09d11227a6215ee5f
- https://git.kernel.org/stable/c/dbd14f736be02cfe73049bd801af89becd1a0749
- https://git.kernel.org/stable/c/f1efff8858403191361a01269c6fe8dd7f55a385