CVE Catalog

CVE-2026-31680

HighCVSS 7.8
Published: Updated: Translated: NVD NIST

Exploitation Probability (EPSS)

Low risk
0.12%

2th percentile - higher than 2% of all known CVEs

Summary

In the Linux kernel, a vulnerability was found in the IPv6 flowlabel mechanism. The `ip6fl_seq_show()` function reads from the global flowlabel hash under RCU protection, but exclusive flowlabels freed `fl->opt` immediately when `fl->users` dropped to zero, while the `ip6_flowlabel` structure remained visible in the hash table. This race condition allowed a concurrent read of `/proc/net/ip6_flowlabel` to access freed memory, causing a system crash.

Risk Assessment

The organization faces the risk of a kernel panic when reading `/proc/net/ip6_flowlabel` while another process releases a flowlabel. This can disrupt critical services and potentially lead to data loss.

Recommendation

Immediately update the Linux kernel to a version containing the fix that delays freeing `fl->opt` until `fl_free_rcu()` is called. Monitor your distribution for the patch and apply it urgently.

Other vulnerabilities in Linux kernel

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Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS