CVE-2026-74621

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: act_ct: fix sk_buff leak when the header checks reject a packet tcf_ct_handle_fragments() runs its header sanity checks before handing anything to the defragmentation engine: if (family == NFPROTO_IPV4) err = tcf_ct_ipv4_is_fragment(skb, &frag); else err = tcf_ct_ipv6_is_fragment(skb, &frag); if (err || !frag) return err; tcf_ct_ipv4_is_fragment() returns -EINVAL or -ENOMEM; tcf_ct_ipv6_is_fragment() adds -EPROTO when ipv6_find_hdr() fails. None of them frees or queues the skb, so on that path the caller still owns it. tcf_ct_act() however funnels every non-zero return into the ownership-transfer exit: err = tcf_ct_handle_fragments(net, skb, family, p->zone, &defrag); if (err) goto out_frag; ... out_frag: if (err != -EINPROGRESS) tcf_action_inc_drop_qstats(&c->common); return TC_ACT_CONSUMED; TC_ACT_CONSUMED means the action took ownership of the skb, so no caller frees it - sch_handle_ingress(), sch_handle_egress() and tcf_qevent_handle() all deliberately skip the free for that verdict. The skb is therefore orphaned: one sk_buff plus its data buffer is leaked per malformed packet, unbounded. Note the drop counter is already incremented for these errors, so the statistics claim a drop that never happens. Three different ownership states reach out_frag: today - the skb may be queued by the defrag engine (-EINPROGRESS), already freed by nf_ct_handle_fragments(), or still owned by us. Tell the caller which of those it is, and free the packet ourselves in the last case, which restores the TC_ACT_SHOT behaviour that predated the Fixes: commit. Reproduced on v7.2-rc6 with a 54-byte frame carrying a 40-byte IPv6 header with nexthdr = 0 (hop-by-hop) and nothing after it, on a clsact ingress chain with "action ct". kmemleak reports one leaked 232-byte skbuff_head_cache object plus its 704-byte data buffer per packet; with this patch it reports none.

Gravité et risque d'exploitation

CVE-2026-74621 obtient un score CVSS de 7.5/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.49 %, ce qui la place devant 40.8 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, <=6.12.*, 6.6.152, <737873a59905a54ca0d2d127ef882f3f88bf4379, 5.15.148, <6.6.152, 5.15.217, <47d99828591d0fe8be4b9c8992ff3b8e47968db9, 0, 0b5b831122fc3789fff75be433ba3e4dd7b779d4, <=7.1.*, 6.6.14, 6.8, <6.8, 6.1.75, <23e97d594ddd0153020c506d5041048fbde1beb4, <b47bb899e04b5407c5a63fe88d4b6676586a6e84, 73f7da5fd124f2cda9161e2e46114915e6e82e97, <=6.6.*, 7.1.9, 3f14b377d01d8357eba032b4cabc8c1149b458b6, <=6.18.*, <5.15.217, 6.1.184, 172ba7d46c202e679f3ccb10264c67416aaeb1c4, <6.1.184, 6.12.104, <8a7ed561671aa6a911a2de99e59ef670a4d0b1df, 6.7.2, f5346df0591d10bc948761ca854b1fae6d2ef441, 6.18.45, <=*, <=5.15.*, <b5dbecc2016e1692fd1c2532af9c41ba729cb747, 7.2, <439d3e404f9d5e515911cc8132cde198b337c19e) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/b5dbecc2016e1692fd1c2532af9c41ba729cb747
• https://git.kernel.org/stable/c/23e97d594ddd0153020c506d5041048fbde1beb4
• https://git.kernel.org/stable/c/737873a59905a54ca0d2d127ef882f3f88bf4379
• https://git.kernel.org/stable/c/47d99828591d0fe8be4b9c8992ff3b8e47968db9
• https://git.kernel.org/stable/c/b47bb899e04b5407c5a63fe88d4b6676586a6e84
• https://git.kernel.org/stable/c/439d3e404f9d5e515911cc8132cde198b337c19e
• https://git.kernel.org/stable/c/8a7ed561671aa6a911a2de99e59ef670a4d0b1df