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CVE-2026-74621— net/sched: act_ct: fix sk_buff leak when the header checks reject a packet

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel 6.8版本存在安全漏洞，该漏洞源于net/sched/act_ct.c中的tcf_ct_handle_fragments()函数在数据包头部检查失败时未释放sk_buff，且tcf_ct_act()将非零返回值视为所有权转移并返回TC_ACT_CONSUMED，导致sk_buff泄漏，可能造成拒绝服务。

CVSS 7.5 · High EPSS 0.49% · P41

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 21

VendorProduct Version RangeStatus
Linux Linux 172ba7d46c202e679f3ccb10264c67416aaeb1c4< b5dbecc2016e1692fd1c2532af9c41ba729cb747 affected
0b5b831122fc3789fff75be433ba3e4dd7b779d4< 23e97d594ddd0153020c506d5041048fbde1beb4 affected
73f7da5fd124f2cda9161e2e46114915e6e82e97< 737873a59905a54ca0d2d127ef882f3f88bf4379 affected
3f14b377d01d8357eba032b4cabc8c1149b458b6< 47d99828591d0fe8be4b9c8992ff3b8e47968db9 affected
3f14b377d01d8357eba032b4cabc8c1149b458b6< b47bb899e04b5407c5a63fe88d4b6676586a6e84 affected
3f14b377d01d8357eba032b4cabc8c1149b458b6< 439d3e404f9d5e515911cc8132cde198b337c19e affected
3f14b377d01d8357eba032b4cabc8c1149b458b6< 8a7ed561671aa6a911a2de99e59ef670a4d0b1df affected
f5346df0591d10bc948761ca854b1fae6d2ef441 affected
… +13 more rows
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I. Basic Information for CVE-2026-74621

Vulnerability Information
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Vulnerability Title
net/sched: act_ct: fix sk_buff leak when the header checks reject a packet
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel 6.8版本存在安全漏洞，该漏洞源于net/sched/act_ct.c中的tcf_ct_handle_fragments()函数在数据包头部检查失败时未释放sk_buff，且tcf_ct_act()将非零返回值视为所有权转移并返回TC_ACT_CONSUMED，导致sk_buff泄漏，可能造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 172ba7d46c202e679f3ccb10264c67416aaeb1c4 ~ b5dbecc2016e1692fd1c2532af9c41ba729cb747 -
Linux Linux 6.8 -

II. Public POCs for CVE-2026-74621

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III. Intelligence Information for CVE-2026-74621

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Patches & Fixes for CVE-2026-74621 (7)

Same Patch Batch · Linux · 2026-08-22 · 149 CVEs total

CVE-2026-74612 10.0 CRITICAL veth: fix skb length accounting after XDP frag adjustment
CVE-2026-74705 10.0 CRITICAL udp: fix potential use-after-free in tunnel segmentation
CVE-2026-74688 9.8 CRITICAL sctp: clear control chunk transport if it is being removed
CVE-2026-74586 9.8 CRITICAL sctp: clear new_transport when removing a peer
CVE-2026-74587 9.8 CRITICAL sctp: fix use-after-free of cached ASCONF chunk
CVE-2026-74588 9.8 CRITICAL sctp: keep chunk->transport in step with the list it is queued on
CVE-2026-74617 9.8 CRITICAL dibs: initialise dibs->lock in dibs_dev_alloc()
CVE-2026-74669 9.8 CRITICAL ipvs: clear IPv4 options after rebasing tunnel ICMP errors
CVE-2026-74591 9.8 CRITICAL mm/filemap: __filemap_add_folio() restore index before retrying
CVE-2026-74616 9.8 CRITICAL xdp: reject clones that overrun skb_shared_info tailroom
CVE-2026-74730 9.8 CRITICAL NFS: Pin the 'struct nfs_server' during a FREE_STATEID call
CVE-2026-74628 9.8 CRITICAL net/x25: fix use-after-free of the socket by its timers
CVE-2026-74611 9.8 CRITICAL tls: rx: restore msg_iter before TLS 1.3 optimistic retry
CVE-2026-74597 9.8 CRITICAL ip6_tunnel: clear skb2->cb[] in ip6ip6_err()
CVE-2026-74608 9.8 CRITICAL smb: client: Fix use-after-free in cifs_try_adding_channels()
CVE-2026-74723 9.8 CRITICAL btrfs: lzo: reject inline extents without valid headers
CVE-2026-74662 9.8 CRITICAL inet: frags: publish queues before arming timer
CVE-2026-74727 9.8 CRITICAL ovpn: skip rehash for peers already removed from by_id
CVE-2026-74712 9.3 CRITICAL vdpa/mlx5: Fix buffer length in create_direct_keys()
CVE-2026-74665 9.1 CRITICAL net: fix skb length accounting after generic XDP frag adjustment

Showing top 20 of 149 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-74621

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