Linux kernel cls_flow NULL deref on shared blocks
CVE-2026-31422 Published on April 13, 2026
net/sched: cls_flow: fix NULL pointer dereference on shared blocks
In the Linux kernel, the following vulnerability has been resolved:
net/sched: cls_flow: fix NULL pointer dereference on shared blocks
flow_change() calls tcf_block_q() and dereferences q->handle to derive
a default baseclass. Shared blocks leave block->q NULL, causing a NULL
deref when a flow filter without a fully qualified baseclass is created
on a shared block.
Check tcf_block_shared() before accessing block->q and return -EINVAL
for shared blocks. This avoids the null-deref shown below:
=======================================================================
KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f]
RIP: 0010:flow_change (net/sched/cls_flow.c:508)
Call Trace:
tc_new_tfilter (net/sched/cls_api.c:2432)
rtnetlink_rcv_msg (net/core/rtnetlink.c:6980)
[...]
=======================================================================
Products Associated with CVE-2026-31422
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Affected Versions
Linux:- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below 57f94ac7e953eece5ed4819605a18f3cdfc63dcc is affected.
- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below 942813276edeb1741fa5b0a73471beb4e495fa08 is affected.
- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below cc707a4fd4c3b6ab2722e06bc359aa010e13d408 is affected.
- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below 4a09f72007201c9f667dc47f64517ec23eea65e5 is affected.
- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below 9bf5fc36a43f7b8b5507c96e74fb81f1e8b4957e is affected.
- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below a208c3e1232997e9317887294c20008dfcb75449 is affected.
- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below 415ea0c973c754b9f375225807810eb9045f4293 is affected.
- Version 1abf272022cf1d18469405f47b4ec49c6a3125db and below 1a280dd4bd1d616a01d6ffe0de284c907b555504 is affected.
- Version 4.15 is affected.
- Before 4.15 is unaffected.
- Version 5.10.253, <= 5.10.* is unaffected.
- Version 5.15.203, <= 5.15.* is unaffected.
- Version 6.1.168, <= 6.1.* is unaffected.
- Version 6.6.134, <= 6.6.* is unaffected.
- Version 6.12.81, <= 6.12.* is unaffected.
- Version 6.18.22, <= 6.18.* is unaffected.
- Version 6.19.12, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.