CVE-2026-31421Medium· 5.5▾ SunlitIn the Linux kernel, the following vulnerability has been resolved: net/sched: cls_fw: fix NULL pointer dereference on shared blocks The old-method path in fw_classify() calls tcf_block_q() and dereferences q->handle. Shared blocks le…
▾ Sunlit zone — Low / medium · no exploitation signal
impact 30.3 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.1%
0.1% → 0.2%
Last analysed / modified upstream
— → 5.5
none → medium
In the Linux kernel, the following vulnerability has been resolved:
net/sched: cls_fw: fix NULL pointer dereference on shared blocks
The old-method path in fw_classify() calls tcf_block_q() and dereferences q->handle. Shared blocks leave block->q NULL, causing a NULL deref when an empty cls_fw filter is attached to a shared block and a packet with a nonzero major skb mark is classified.
Reject the configuration in fw_change() when the old method (no TCA_OPTIONS) is used on a shared block, since fw_classify()'s old-method path needs block->q which is NULL for shared blocks.
The fixed null-ptr-deref calling stack: KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:fw_classify (net/sched/cls_fw.c:81) Call Trace: tcf_classify (./include/net/tc_wrapper.h:197 net/sched/cls_api.c:1764 net/sched/cls_api.c:1860) tc_run (net/core/dev.c:4401) __dev_queue_xmit (net/core/dev.c:4535 net/core/dev.c:4790)
linux_kernel >= 4.15, < 5.10.253linux_kernel >= 5.11, < 5.15.203linux_kernel >= 5.16, < 6.1.168linux_kernel >= 6.2, < 6.6.134linux_kernel >= 6.7, < 6.12.81linux_kernel >= 6.13, < 6.18.22linux_kernel >= 6.19, < 6.19.12linux_kernel = 7.0Upgrade past the affected range:
linux_kernel 6.19.12Field changes observed since this record was first indexed.
Connected by shared product, vendor, weakness, or advisory.
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