CVE-2026-31680
Received Received - Intake
Use-After-Free in Linux Kernel IPv6 Flowlabel Causes Crash

Publication date: 2026-04-25

Last updated on: 2026-05-06

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net: ipv6: flowlabel: defer exclusive option free until RCU teardown `ip6fl_seq_show()` walks the global flowlabel hash under the seq-file RCU read-side lock and prints `fl->opt->opt_nflen` when an option block is present. Exclusive flowlabels currently free `fl->opt` as soon as `fl->users` drops to zero in `fl_release()`. However, the surrounding `struct ip6_flowlabel` remains visible in the global hash table until later garbage collection removes it and `fl_free_rcu()` finally tears it down. A concurrent `/proc/net/ip6_flowlabel` reader can therefore race that early `kfree()` and dereference freed option state, triggering a crash in `ip6fl_seq_show()`. Fix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches the lifetime already required for the enclosing flowlabel while readers can still reach it under RCU.
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Meta Information
Published
2026-04-25
Last Modified
2026-05-06
Generated
2026-06-16
AI Q&A
2026-04-26
EPSS Evaluated
2026-06-15
NVD
CVE-2026-31680
Affected Vendors & Products
Showing 13 associated CPEs
Vendor Product Version / Range
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel 7.0
linux linux_kernel From 5.11 (inc) to 5.15.203 (exc)
linux linux_kernel From 6.13 (inc) to 6.18.22 (exc)
linux linux_kernel From 5.16 (inc) to 6.1.168 (exc)
linux linux_kernel From 6.19 (inc) to 6.19.12 (exc)
linux linux_kernel From 6.7 (inc) to 6.12.81 (exc)
linux linux_kernel From 6.2 (inc) to 6.6.134 (exc)
linux linux_kernel From 3.9 (inc) to 5.10.253 (exc)
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Exploitability
CWE
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability exists in the Linux kernel's IPv6 flowlabel handling. Specifically, it involves a race condition where an option block associated with a flowlabel is freed too early. The function ip6fl_seq_show() reads flowlabel options under a read-copy-update (RCU) lock, but the option block (fl->opt) is freed as soon as the user count drops to zero, even though the flowlabel structure remains visible in the global hash table until later garbage collection. This can cause a concurrent reader of /proc/net/ip6_flowlabel to access freed memory, leading to a crash.

Impact Analysis

The primary impact of this vulnerability is a potential system crash caused by a use-after-free condition when reading IPv6 flowlabel information. This can lead to denial of service (DoS) as the kernel may crash or become unstable when a concurrent process accesses freed memory.

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