# CVE-2026-98099: ipv6: mcast: use rcu_assign_pointer() for __rcu list updates

CVE-2026-98099 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-98099, released October 2, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-98099
- Priority: High
- CVSS: 7.1 (Moderate)
- EPSS: 0.0009
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 25, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98099

## 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().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-98099](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98099.md) | Oct 2, 2026 |
| Linux | linux Debian 14 | 7.2.7-1 | [DEBIAN-CVE-2026-98099](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98099.md) | Oct 2, 2026 |

---

Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.