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CVE-2025-21765 is a lifetime-management flaw in the Linux kernel IPv6 stack. The ip6_default_advmss() function accessed a network namespace structure without RCU read-side protection. Concurrent teardown could therefore cause the referenced structure to disappear while it was being read. The upstream correction adds RCU protection around the access.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Linux kernel IPv6 RCU synchronization flaw.
A Linux kernel IPv6 flaw in ip6_default_advmss() caused by missing RCU protection while reading a network structure, creating a potential use-after-free/race condition. The issue has been resolved upstream and through Red Hat advisories for Red Hat Enterprise Linux 9 and 10.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.