FlawAtlas
Search the atlas
UBUNTU-CVE-2025-40214 High

UBUNTU-CVE-2025-40214

In the Linux kernel, the following vulnerability has been resolved: af_unix: Initialise scc_index in unix_add_edge(). Quang Le reported that the AF_UNIX GC could garbage-collect a receive queue of an alive in-flight socket, with a nice repro. The repro consists of three stages. 1) 1-a. Create a single cyclic reference with many sockets 1-b. close() all sockets 1-c. Trigger GC 2) 2-a. Pass sk-A to an embryo sk-B 2-b. Pass sk-X to sk-X 2-c. Trigger GC 3) 3-a. accept() the embryo sk-B 3-b. Pass sk-B to sk-C 3-c. close() the in-flight sk-A 3-d. Trigger GC As of 2-c, sk-A and sk-X are linked to unix_unvisited_vertices, and unix_walk_scc() groups them into two different SCCs: unix_sk(sk-A)->vertex->scc_index = 2 (UNIX_VERTEX_INDEX_START) unix_sk(sk-X)->vertex->scc_index = 3 Once GC completes, unix_graph_grouped is set to true. Also, unix_graph_maybe_cyclic is set to true due to sk-X's cyclic self-reference, which makes close() trigger GC. At 3-b, unix_add_edge() allocates unix_sk(sk-B)->vertex and links it to unix_unvisited_vertices. unix_update_graph() is called at 3-a. and 3-b., but neither unix_graph_grouped nor unix_graph_maybe_cyclic is changed because both sk-B's listener and sk-C are not in-flight. 3-c decrements sk-A's file refcnt to 1. Since unix_graph_grouped is true at 3-d, unix_walk_scc_fast() is finally called and iterates 3 sockets sk-A, sk-B, and sk-X: sk-A -> sk-B (-> sk-C) sk-X -> sk-X This is totally fine. All of them are not yet close()d and should be grouped into different SCCs. However, unix_vertex_dead() misjudges that sk-A and sk-B are in the same SCC and sk-A is dead. unix_sk(sk-A)->scc_index == unix_sk(sk-B)->scc_index <-- Wrong! && sk-A's file refcnt == unix_sk(sk-A)->vertex->out_degree ^-- 1 in-flight count for sk-B -> sk-A is dead !? The problem is that unix_add_edge() does not initialise scc_index. Stage 1) is used for heap spraying, making a newly allocated vertex have vertex->scc_index == 2 (UNIX_VERTEX_INDEX_START) set by unix_walk_scc() at 1-c. Let's track the max SCC index from the previous unix_walk_scc() call and assign the max + 1 to a new vertex's scc_index. This way, we can continue to avoid Tarjan's algorithm while preventing misjudgments.

Exploit probability Not scored
Published December 4, 2025
Required by Not available
Last source change August 17, 2026

02 / AFFECTED SOFTWARE

Affected packages

Ubuntu:22.04:LTS linux-starfive-6.5

11 explicit affected versions

Ubuntu:18.04:LTS linux-oem

50 explicit affected versions

Ubuntu:18.04:LTS linux-aws-5.0

6 explicit affected versions

Ubuntu:20.04:LTS linux-aws-5.11

12 explicit affected versions

Ubuntu:22.04:LTS linux-oem-6.5

19 explicit affected versions

Ubuntu:24.04:LTS linux-hwe-6.14

10 explicit affected versions

Ubuntu:20.04:LTS linux-raspi2

6 explicit affected versions

Ubuntu:24.04:LTS linux-riscv

24 explicit affected versions

Ubuntu:22.04:LTS linux-riscv-6.5

10 explicit affected versions

Ubuntu:24.04:LTS linux-oem-6.8

26 explicit affected versions

Ubuntu:22.04:LTS linux-azure-5.19

7 explicit affected versions

Ubuntu:22.04:LTS linux-gcp-6.5

13 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.14

35 explicit affected versions

Ubuntu:20.04:LTS linux-gke-5.15

18 explicit affected versions

Ubuntu:20.04:LTS linux-aws-5.13

13 explicit affected versions

Ubuntu:20.04:LTS linux-aws-5.8

4 explicit affected versions

Ubuntu:16.04:LTS linux-hwe-edge

23 explicit affected versions

Ubuntu:24.04:LTS linux-raspi-realtime

1 explicit affected versions

Ubuntu:20.04:LTS linux-hwe-5.8

21 explicit affected versions

Ubuntu:20.04:LTS linux-hwe-5.13

16 explicit affected versions

Ubuntu:22.04:LTS linux-lowlatency-hwe-6.2

10 explicit affected versions

Ubuntu:25.10 linux

11 explicit affected versions

Ubuntu:24.04:LTS linux-hwe-6.11

8 explicit affected versions

Ubuntu:18.04:LTS linux-oracle-5.0

7 explicit affected versions

Ubuntu:20.04:LTS linux-riscv

12 explicit affected versions

Ubuntu:24.04:LTS linux-oracle-6.14

11 explicit affected versions

Ubuntu:24.04:LTS linux-azure-6.11

7 explicit affected versions

Ubuntu:20.04:LTS linux-gcp-5.11

12 explicit affected versions

Ubuntu:22.04:LTS linux-azure-6.5

14 explicit affected versions

Ubuntu:25.10 linux-azure-fde

10 explicit affected versions

Ubuntu:22.04:LTS linux-intel-iot-realtime

1 explicit affected versions

Ubuntu:20.04:LTS linux-intel-5.13

7 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.13

12 explicit affected versions

Ubuntu:24.04:LTS linux-oracle-6.17

1 explicit affected versions

Ubuntu:20.04:LTS linux-oracle-5.11

12 explicit affected versions

Ubuntu:24.04:LTS linux-oem-6.14

16 explicit affected versions

Ubuntu:25.10 linux-gcp

8 explicit affected versions

Ubuntu:18.04:LTS linux-hwe-edge

10 explicit affected versions

Ubuntu:18.04:LTS linux-gke-5.4

37 explicit affected versions

Ubuntu:24.04:LTS linux-gcp-6.17

1 explicit affected versions

Ubuntu:22.04:LTS linux-oracle-6.5

13 explicit affected versions

Ubuntu:24.04:LTS linux-azure-nvidia-6.14

3 explicit affected versions

Ubuntu:22.04:LTS linux-azure-fde-6.2

10 explicit affected versions

Ubuntu:24.04:LTS linux-gcp-6.14

11 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.10

26 explicit affected versions

Ubuntu:20.04:LTS linux-gcp-5.13

13 explicit affected versions

Ubuntu:20.04:LTS linux-oem-5.6

29 explicit affected versions

Ubuntu:18.04:LTS linux-gcp-5.3

13 explicit affected versions

Ubuntu:24.04:LTS linux-riscv-6.14

12 explicit affected versions

Ubuntu:18.04:LTS linux-gke-4.15

33 explicit affected versions

Ubuntu:22.04:LTS linux-riscv

23 explicit affected versions

Ubuntu:18.04:LTS linux-aws-5.3

10 explicit affected versions

Ubuntu:Nvidia-BlueField:24.04:LTS linux-bluefield

11 explicit affected versions

Ubuntu:24.04:LTS linux-azure-fde-6.14

5 explicit affected versions

Ubuntu:20.04:LTS linux-hwe-5.11

12 explicit affected versions

Ubuntu:Pro:Realtime:24.04:LTS linux-realtime-6.17

1 explicit affected versions

Ubuntu:20.04:LTS linux-azure-5.8

7 explicit affected versions

Ubuntu:22.04:LTS linux-gcp-6.2

12 explicit affected versions

Ubuntu:25.10 linux-azure

7 explicit affected versions

Ubuntu:24.04:LTS linux-azure-6.14

5 explicit affected versions

Ubuntu:22.04:LTS linux-lowlatency-hwe-5.19

10 explicit affected versions

Ubuntu:22.04:LTS linux-oem-5.17

26 explicit affected versions

Ubuntu:24.04:LTS linux-aws-6.14

11 explicit affected versions

Ubuntu:24.04:LTS linux-aws-6.17

1 explicit affected versions

Ubuntu:22.04:LTS linux-azure-6.2

13 explicit affected versions

Ubuntu:22.04:LTS linux-oem-6.0

16 explicit affected versions

Ubuntu:22.04:LTS linux-azure-fde-5.19

3 explicit affected versions

Ubuntu:24.04:LTS linux-gcp-6.11

7 explicit affected versions

Ubuntu:25.10 linux-riscv

6 explicit affected versions

Ubuntu:20.04:LTS linux-gke

51 explicit affected versions

Ubuntu:25.10 linux-oracle

7 explicit affected versions

Ubuntu:24.04:LTS linux-oem-6.11

18 explicit affected versions

Ubuntu:20.04:LTS linux-azure-5.13

12 explicit affected versions

Ubuntu:24.04:LTS linux-nvidia-6.17

1 explicit affected versions

Ubuntu:22.04:LTS linux-oem-6.1

27 explicit affected versions

Ubuntu:22.04:LTS linux-gcp-5.19

8 explicit affected versions

Ubuntu:20.04:LTS linux-oracle-5.8

5 explicit affected versions

Ubuntu:22.04:LTS linux-riscv-5.19

8 explicit affected versions

Ubuntu:22.04:LTS linux-hwe-6.2

10 explicit affected versions

Ubuntu:24.04:LTS linux-lowlatency-hwe-6.11

7 explicit affected versions

Ubuntu:22.04:LTS linux-lowlatency-hwe-6.5

13 explicit affected versions

Ubuntu:20.04:LTS linux-azure-5.11

13 explicit affected versions

Ubuntu:22.04:LTS linux-starfive-5.19

7 explicit affected versions

Ubuntu:24.04:LTS linux-nvidia-6.11

8 explicit affected versions

Ubuntu:20.04:LTS linux-riscv-5.8

10 explicit affected versions

Ubuntu:20.04:LTS linux-oracle-5.13

12 explicit affected versions

Ubuntu:Pro:Realtime:24.04:LTS linux-realtime-6.14

9 explicit affected versions

Ubuntu:18.04:LTS linux-azure

44 explicit affected versions

Ubuntu:18.04:LTS linux-azure-5.3

16 explicit affected versions

Ubuntu:22.04:LTS linux-starfive-6.2

3 explicit affected versions

Ubuntu:20.04:LTS linux-riscv-5.11

13 explicit affected versions

Ubuntu:20.04:LTS linux-azure-fde

26 explicit affected versions

Ubuntu:20.04:LTS linux-gkeop-5.15

45 explicit affected versions

Ubuntu:18.04:LTS linux-gkeop-5.4

37 explicit affected versions

Ubuntu:22.04:LTS linux-aws-6.5

14 explicit affected versions

Ubuntu:18.04:LTS linux-gcp

38 explicit affected versions

Ubuntu:18.04:LTS linux-oracle-5.3

9 explicit affected versions

Ubuntu:25.10 linux-aws

8 explicit affected versions

Ubuntu:22.04:LTS linux-hwe-5.19

11 explicit affected versions

Ubuntu:25.10 linux-raspi

5 explicit affected versions

Ubuntu:22.04:LTS linux-nvidia-6.2

7 explicit affected versions

Ubuntu:20.04:LTS linux-gcp-5.8

4 explicit affected versions

Ubuntu:24.04:LTS linux-realtime

1 explicit affected versions

Ubuntu:22.04:LTS linux-hwe-6.5

13 explicit affected versions

Ubuntu:18.04:LTS linux-hwe

43 explicit affected versions

Ubuntu:24.04:LTS linux-oem-6.17

5 explicit affected versions

Ubuntu:22.04:LTS linux-aws-5.19

10 explicit affected versions

Ubuntu:22.04:LTS linux-allwinner-5.19

8 explicit affected versions

Ubuntu:22.04:LTS linux-aws-6.2

14 explicit affected versions

Ubuntu:18.04:LTS linux-azure-edge

4 explicit affected versions

Ubuntu:20.04:LTS linux-gkeop

78 explicit affected versions

Ubuntu:25.10 linux-realtime

5 explicit affected versions

Ubuntu:22.04:LTS linux-nvidia-6.5

11 explicit affected versions

Ubuntu:22.04:LTS linux-realtime

1 explicit affected versions

03 / CONNECTIONS

Connected vulnerabilities

04 / EVIDENCE

Source records

Open Source Vulnerabilities UBUNTU-CVE-2025-40214

In the Linux kernel, the following vulnerability has been resolved: af_unix: Initialise scc_index in unix_add_edge(). Quang Le reported that the AF_UNIX GC could garbage-collect a receive queue of an alive in-flight socket, with a nice repro. The repro consists of three stages. 1) 1-a. Create a single cyclic reference with many sockets 1-b. close() all sockets 1-c. Trigger GC 2) 2-a. Pass sk-A to an embryo sk-B 2-b. Pass sk-X to sk-X 2-c. Trigger GC 3) 3-a. accept() the embryo sk-B 3-b. Pass sk-B to sk-C 3-c. close() the in-flight sk-A 3-d. Trigger GC As of 2-c, sk-A and sk-X are linked to unix_unvisited_vertices, and unix_walk_scc() groups them into two different SCCs: unix_sk(sk-A)->vertex->scc_index = 2 (UNIX_VERTEX_INDEX_START) unix_sk(sk-X)->vertex->scc_index = 3 Once GC completes, unix_graph_grouped is set to true. Also, unix_graph_maybe_cyclic is set to true due to sk-X's cyclic self-reference, which makes close() trigger GC. At 3-b, unix_add_edge() allocates unix_sk(sk-B)->vertex and links it to unix_unvisited_vertices. unix_update_graph() is called at 3-a. and 3-b., but neither unix_graph_grouped nor unix_graph_maybe_cyclic is changed because both sk-B's listener and sk-C are not in-flight. 3-c decrements sk-A's file refcnt to 1. Since unix_graph_grouped is true at 3-d, unix_walk_scc_fast() is finally called and iterates 3 sockets sk-A, sk-B, and sk-X: sk-A -> sk-B (-> sk-C) sk-X -> sk-X This is totally fine. All of them are not yet close()d and should be grouped into different SCCs. However, unix_vertex_dead() misjudges that sk-A and sk-B are in the same SCC and sk-A is dead. unix_sk(sk-A)->scc_index == unix_sk(sk-B)->scc_index <-- Wrong! && sk-A's file refcnt == unix_sk(sk-A)->vertex->out_degree ^-- 1 in-flight count for sk-B -> sk-A is dead !? The problem is that unix_add_edge() does not initialise scc_index. Stage 1) is used for heap spraying, making a newly allocated vertex have vertex->scc_index == 2 (UNIX_VERTEX_INDEX_START) set by unix_walk_scc() at 1-c. Let's track the max SCC index from the previous unix_walk_scc() call and assign the max + 1 to a new vertex's scc_index. This way, we can continue to avoid Tarjan's algorithm while preventing misjudgments.

View original source

05 / REFERENCES

Further evidence