VulnerabilityPublished 25 Sep 2026Updated 19 Oct 2026

CVE-2026-98101: Linux kernel · ipv6: mcast: use copy-on-write RCU updates in ip6_mc_source()

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in dba00514bf668c26cb4900e9f0da84bf96bf065a : update Linux kernel when convenient.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in dba00514bf668c26cb4900e9f0da84bf96bf065a, c073d1b070f171d206b19c98d71739a97f15b3f1, ac51321d3b2391860a935820ebcf4d8b9bb16a8a +3

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected >=5.10.261 <5.11	Fixed in dba00514bf668c26cb4900e9f0da84bf96bf065a c073d1b070f171d206b19c98d71739a97f15b3f1 ac51321d3b2391860a935820ebcf4d8b9bb16a8a 20db91a052332ef5552bd2f651ffb9db911cf67b 5.11 2c2091e2ee93049fc513ad1e6c99d8b6c809f467
LinuxLinux	Affected =5.13	Fixed in–

AI-suggested

A fix is available in Linux kernel version 5.11 and later, as well as in the 5.13 release. Users and administrators should upgrade affected Linux kernel versions to 5.11 or 5.13 or later to remediate this issue. No additional mitigation steps are indicated.

Description

A vulnerability in the Linux kernel's IPv6 multicast source filter handling was fixed by changing to copy-on-write RCU updates in the ip6_mc_source() function. The flaw involved unsynchronized in-place mutation of source filter data structures, which could cause concurrent readers to observe torn IPv6 addresses or inconsistent source entries. This issue affects certain Linux kernel versions prior to 5.11 and version 5.13. The fix involves allocating and fully populating new filter data before publishing it, ensuring safe concurrent reads.

Impact

The vulnerability could lead to inconsistent or corrupted IPv6 multicast source filter data being observed by concurrent readers in the UDP and RAW multicast receive paths. This may cause incorrect multicast packet processing due to torn or duplicated IPv6 addresses in source filters. There is no indication of direct code execution or privilege escalation. No known exploits in the wild have been reported.

Summary

CVE-2026-98101 addresses a concurrency flaw in the Linux kernel's IPv6 multicast source filter code. The ip6_mc_source() function previously mutated source filter entries in-place without proper synchronization, while readers accessed these entries locklessly under RCU read locks. Because 16-byte IPv6 address writes are not atomic and array shifts were unsynchronized, readers could see torn or duplicated source entries. The fix switches to a copy-on-write approach, fully preparing new filter data before publishing it with rcu_assign_pointer(), and freeing old data with kfree_rcu(), aligning with safe RCU update patterns.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 12:42 UTC

Technical details

References

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