{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-21958","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-12-29T08:45:45.791Z","datePublished":"2025-04-01T15:46:57.268Z","dateUpdated":"2026-08-05T11:55:36.868Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T11:55:36.868Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nRevert \"openvswitch: switch to per-action label counting in conntrack\"\n\nCurrently, ovs_ct_set_labels() is only called for confirmed conntrack\nentries (ct) within ovs_ct_commit(). However, if the conntrack entry\ndoes not have the labels_ext extension, attempting to allocate it in\novs_ct_get_conn_labels() for a confirmed entry triggers a warning in\nnf_ct_ext_add():\n\n  WARN_ON(nf_ct_is_confirmed(ct));\n\nThis happens when the conntrack entry is created externally before OVS\nincrements net->ct.labels_used. The issue has become more likely since\ncommit fcb1aa5163b1 (\"openvswitch: switch to per-action label counting\nin conntrack\"), which changed to use per-action label counting and\nincrement net->ct.labels_used when a flow with ct action is added.\n\nSince there’s no straightforward way to fully resolve this issue at the\nmoment, this reverts the commit to avoid breaking existing use cases."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - Triggering requires installing an OVS datapath flow carrying a ct action with a non-zero label mask via the openvswitch generic-netlink interface, which is a local operation. Although the packet that fires the bug can arrive from the wire on an OVS/OVN host, the necessary local netlink configuration step makes Local the defensible vector.\nAC:L - The attacker fully controls the ordering that creates the bug — create the conntrack entry while net->ct.labels_used is zero, then install the ct-label flow, then re-send a packet of that connection — and equally controls the concurrent traffic that turns the krealloc of a hash-visible ct->ext into a use-after-free. No condition lies outside attacker influence.\nPR:L - All OVS datapath/flow/vport netlink commands use GENL_UNS_ADMIN_PERM, i.e. CAP_NET_ADMIN in the netns owner user namespace, which any unprivileged user obtains with unshare -Urn; nftables in the same namespace supplies the externally created conntrack entry.\nUI:N - The attacker performs every step — namespace setup, flow installation and packet injection — with no action from any other user.\nS:U - The corruption is confined to kernel heap objects belonging to the same kernel security authority; no VM, IOMMU or sandbox boundary is crossed.\nC:H - nf_ct_ext_add() reallocates ct->ext on a confirmed, hash-table-visible conntrack with no RCU grace period, so lock-free readers such as nf_conn_acct_find(), nfct_nat(), nf_ct_ecache_find() and nf_ct_labels_find() dereference freed memory, giving a use-after-free read that can be groomed to disclose arbitrary kernel heap contents.\nI:H - The same window is a use-after-free write — nf_ct_acct_update() performs atomic64_add() into the freed extension block, and nf_ct_ext_add() itself writes offsets and memsets into a buffer another CPU may already have reallocated — yielding heap corruption exploitable for control-flow hijack.\nA:H - The WARN_ON(nf_ct_is_confirmed(ct)) splat is an immediate kernel warning that panics the machine under panic_on_warn, and the underlying use-after-free readily causes oopses and slab corruption crashes."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/openvswitch/conntrack.c","net/openvswitch/datapath.h"],"versions":[{"version":"fcb1aa5163b1ae4cf2864b688b08927aac51f51e","lessThan":"9e79fdabd52cfce1a021640a81256878a2c516a2","status":"affected","versionType":"git"},{"version":"fcb1aa5163b1ae4cf2864b688b08927aac51f51e","lessThan":"d91bfc64a4886102746e74d2c6f3a61e9a77fd7d","status":"affected","versionType":"git"},{"version":"fcb1aa5163b1ae4cf2864b688b08927aac51f51e","lessThan":"1063ae07383c0ddc5bcce170260c143825846b03","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/openvswitch/conntrack.c","net/openvswitch/datapath.h"],"versions":[{"version":"6.12","status":"affected"},{"version":"0","lessThan":"6.12","status":"unaffected","versionType":"semver"},{"version":"6.12.20","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.13.8","lessThanOrEqual":"6.13.*","status":"unaffected","versionType":"semver"},{"version":"6.14","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12","versionEndExcluding":"6.12.20"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12","versionEndExcluding":"6.13.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12","versionEndExcluding":"6.14"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/9e79fdabd52cfce1a021640a81256878a2c516a2"},{"url":"https://git.kernel.org/stable/c/d91bfc64a4886102746e74d2c6f3a61e9a77fd7d"},{"url":"https://git.kernel.org/stable/c/1063ae07383c0ddc5bcce170260c143825846b03"}],"title":"Revert \"openvswitch: switch to per-action label counting in conntrack\"","x_generator":{"engine":"bippy-1.2.0"}}}}