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CVE-2026-74621

net/sched: act_ct: fix sk_buff leak when the header checks reject a packet

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.15.217, 6.1.184, 6.6.152, 6.8, 6.12.104, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: yes
  • Technical impact: partial

Summary

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: yes · Technical impact: partial

  3. Record last updated

Affected versions

  • Linux Linux

    From 172ba7d46c202e679f3ccb10264c67416aaeb1c4 · fixed in b5dbecc2016e1692fd1c2532af9c41ba729cb747; From 0b5b831122fc3789fff75be433ba3e4dd7b779d4 · fixed in 23e97d594ddd0153020c506d5041048fbde1beb4; From 73f7da5fd124f2cda9161e2e46114915e6e82e97 · fixed in 737873a59905a54ca0d2d127ef882f3f88bf4379; From 3f14b377d01d8357eba032b4cabc8c1149b458b6 · fixed in 47d99828591d0fe8be4b9c8992ff3b8e47968db9; From 3f14b377d01d8357eba032b4cabc8c1149b458b6 · fixed in b47bb899e04b5407c5a63fe88d4b6676586a6e84; From 3f14b377d01d8357eba032b4cabc8c1149b458b6 · fixed in 439d3e404f9d5e515911cc8132cde198b337c19e; From 3f14b377d01d8357eba032b4cabc8c1149b458b6 · fixed in 8a7ed561671aa6a911a2de99e59ef670a4d0b1df; From 5.15.148 · fixed in 5.15.217; From 6.1.75 · fixed in 6.1.184; From 6.6.14 · fixed in 6.6.152; From 6.7.2 · fixed in 6.8

  • Linux Linux

    6.8

  • KernelLinux

    fixed in 5.15.217; From 5.16.0 · fixed in 6.1.184; From 6.2.0 · fixed in 6.6.152; From 6.7.0 · fixed in 6.12.104; From 6.8.0 · fixed in 6.18.45; From 6.13.0 · fixed in 7.1.9

References 7

git.kernel.org