Summary
In the Linux kernel, the following vulnerability has been resolved: af_unix: Don't leave...
In 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:
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
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---
Impact
Memory is accessed after it has been freed, leading to undefined behavior in native code. Typical impact: memory corruption, crash, or potential code execution.
CVE-2025-38236 has a CVSS score of 7.8 (High). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-38236? CVE-2025-38236 is a high-severity use after free vulnerability. No fixed version is listed yet. Memory is accessed after it has been freed, leading to undefined behavior in native code.
- How severe is CVE-2025-38236? CVE-2025-38236 has a CVSS score of 7.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-38236? No fixed version is listed for CVE-2025-38236 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-38236 exploitable, and should I be worried? Whether CVE-2025-38236 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-38236 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.