CVE-2025-38236 — linux / linux_kernel
Use After FreeIn the Linux kernel, the following vulnerability has been resolved:
af_unix: Don't leave consecutive consumed OOB skbs.
Jann Horn reported a use-after-free in unix_stream_read_generic().
The following sequences reproduce the issue:
$ python3 from socket import * s1, s2 = socketpair(AF_UNIX, SOCK_STREAM) s1.send(b'x', MSG_OOB) s2.recv(1, MSG_OOB) # leave a consumed OOB skb s1.send(b'y', MSG_OOB) s2.recv(1, MSG_OOB) # leave a consumed OOB skb s1.send(b'z', MSG_OOB) s2.recv(1) # recv 'z' illegally s2.recv(1, MSG_OOB) # access 'z' skb (use-after-free)
Even though a user reads OOB data, the skb holding the data stays on the recv queue to mark the OOB boundary and break the next recv().
After the last send() in the scenario above, the sk2's recv queue has 2 leading consumed OOB skbs and 1 real OOB skb.
Then, the following happens during the next recv() without MSG_OOB
- unix_stream_read_generic() peeks the first consumed OOB skb
- manage_oob() returns the next consumed OOB skb
- unix_stream_read_generic() fetches the next not-yet-consumed OOB skb
- unix_stream_read_generic() reads and frees the OOB skb
, and the last recv(MSG_OOB) triggers KASAN splat.
The 3. above occurs because of the SO_PEEK_OFF code, which does not expect unix_skb_len(skb) to be 0, but this is true for such consumed OOB skbs.
while (skip >= unix_skb_len(skb)) { skip -= unix_skb_len(skb); skb = skb_peek_next(skb, &sk->sk_receive_queue); ... }
In addition to this use-after-free, there is another issue that ioctl(SIOCATMARK) does not function properly with consecutive consumed OOB skbs.
So, nothing good comes out of such a situation.
Instead of complicating manage_oob(), ioctl() handling, and the next ECONNRESET fix by introducing a loop for consecutive consumed OOB skbs, let's not leave such consecutive OOB unnecessarily.
Now, while receiving an OOB skb in unix_stream_recv_urg(), if its previous skb is a consumed OOB skb, it is freed.
[0]: BUG: KASAN: slab-use-after-free in unix_stream_read_actor (net/unix/af_unix.c:3027) Read of size 4 at addr ffff888106ef2904 by task python3/315
CPU: 2 UID: 0 PID: 315 Comm: python3 Not tainted 6.16.0-rc1-00407-gec315832f6f9 #8 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-4.fc42 04/01/2014 Call Trace: <TASK> dump_stack_lvl (lib/dump_stack.c:122) print_report (mm/kasan/report.c:409 mm/kasan/report.c:521) kasan_report (mm/kasan/report.c:636) unix_stream_read_actor (net/unix/af_unix.c:3027) unix_stream_read_generic (net/unix/af_unix.c:2708 net/unix/af_unix.c:2847) unix_stream_recvmsg (net/unix/af_unix.c:3048) sock_recvmsg (net/socket.c:1063 (discriminator 20) net/socket.c:1085 (discriminator 20)) __sys_recvfrom (net/socket.c:2278) __x64_sys_recvfrom (net/socket.c:2291 (discriminator 1) net/socket.c:2287 (discriminator 1) net/socket.c:2287 (discriminator 1)) do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1)) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f8911fcea06 Code: 5d e8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 75 19 83 e2 39 83 fa 08 75 11 e8 26 ff ff ff 66 0f 1f 44 00 00 48 8b 45 10 0f 05 <48> 8b 5d f8 c9 c3 0f 1f 40 00 f3 0f 1e fa 55 48 89 e5 48 83 ec 08 RSP: 002b:00007fffdb0dccb0 EFLAGS: 00000202 ORIG_RAX: 000000000000002d RAX: ffffffffffffffda RBX: 00007fffdb0dcdc8 RCX: 00007f8911fcea06 RDX: 0000000000000001 RSI: 00007f8911a5e060 RDI: 0000000000000006 RBP: 00007fffdb0dccd0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000202 R12: 00007f89119a7d20 R13: ffffffffc4653600 R14: 0000000000000000 R15: 0000000000000000 </TASK>
Allocated by task 315: kasan_save_stack (mm/kasan/common.c:48) kasan_save_track (mm/kasan/common.c:60 (discriminator 1) mm/kasan/common.c:69 (discriminator 1)) _kasan_slab_alloc (mm/kasan/common.c:348) kmem_cache_alloc ---truncated---
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | 5.15 | 5.15.194 |
| linux / linux_kernel | 5.16 | 6.1.143 |
| linux / linux_kernel | 6.2 | 6.6.96 |
| linux / linux_kernel | 6.7 | 6.12.36 |
| linux / linux_kernel | 6.13 | 6.15.5 |
| linux / linux_kernel | 6.16-rc1 | 6.16-rc1.x |
| linux / linux_kernel | 6.16-rc2 | 6.16-rc2.x |
| linux / linux_kernel | 6.16-rc3 | 6.16-rc3.x |
| debian / debian_linux | 11.0 | 11.0.x |
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
- https://git.kernel.org/stable/c/32ca245464e1479bfea8592b9db227fdc1641705
- https://git.kernel.org/stable/c/523edfed4f68b7794d85b9ac828c5f8f4442e4c5
- https://git.kernel.org/stable/c/61a9ad7b69ce688697e5f63332f03e17725353bc
- https://git.kernel.org/stable/c/8db4d2d026e6e3649832bfe23b96c4acff0756db
- https://git.kernel.org/stable/c/a12237865b48a73183df252029ff5065d73d305e
- https://git.kernel.org/stable/c/fad0a2c16062ac7c606b93166a7ce9d265bab976
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
- https://project-zero.issues.chromium.org/issues/423023990
Deep Security Visibility Without the Complexity
SynScan provides clear, real-time security insights so you can monitor your attack surface, spot risks early, and act fast—without extra complexity.
- No setup fees
- 5-min deployment
- Cancel anytime
Frequently Asked Questions
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.