CVE-2025-37756

Published May 1, 2025

Last updated 7 months ago

CVSS medium 5.5

Overview

AI description

Automated description summarized from trusted sources.

CVE-2025-37756 describes a vulnerability within the Linux kernel's TLS (Transport Layer Security) subsystem. The issue, identified by syzbot, stemmed from the ability to disconnect a TLS socket, which could lead to various unexpected scenarios and trigger warnings within the kernel, specifically in `tls_strp.c`. To address this, the resolution involved explicitly disallowing the `disconnect` operation for TLS sockets, as properly supporting this functionality, particularly with offload enabled, was deemed complex due to the need to ensure all packets are acknowledged. Subsequently, a related vulnerability emerged that acts as a bypass for the CVE-2025-37756 patch. This bypass affects the Linux kernel's KTLS (Kernel TLS) subsystem when it interacts with BPF sockmap. The bypass can be triggered by draining the `skb` using BPF, mirroring the `tcp_disconnect` behavior associated with the original CVE-2025-37756. The underlying flaw in this bypass involves the kernel's handling of KTLS and BPF sockmaps, where the `tls_init` path fails to verify if a socket is already linked to a sockmap, potentially allowing exploitation by a malicious user.

Description
In the Linux kernel, the following vulnerability has been resolved: net: tls: explicitly disallow disconnect syzbot discovered that it can disconnect a TLS socket and then run into all sort of unexpected corner cases. I have a vague recollection of Eric pointing this out to us a long time ago. Supporting disconnect is really hard, for one thing if offload is enabled we'd need to wait for all packets to be _acked_. Disconnect is not commonly used, disallow it. The immediate problem syzbot run into is the warning in the strp, but that's just the easiest bug to trigger: WARNING: CPU: 0 PID: 5834 at net/tls/tls_strp.c:486 tls_strp_msg_load+0x72e/0xa80 net/tls/tls_strp.c:486 RIP: 0010:tls_strp_msg_load+0x72e/0xa80 net/tls/tls_strp.c:486 Call Trace: <TASK> tls_rx_rec_wait+0x280/0xa60 net/tls/tls_sw.c:1363 tls_sw_recvmsg+0x85c/0x1c30 net/tls/tls_sw.c:2043 inet6_recvmsg+0x2c9/0x730 net/ipv6/af_inet6.c:678 sock_recvmsg_nosec net/socket.c:1023 [inline] sock_recvmsg+0x109/0x280 net/socket.c:1045 __sys_recvfrom+0x202/0x380 net/socket.c:2237
Source
416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status
Analyzed
Products
linux_kernel, debian_linux

Risk scores

CVSS 3.1

Type
Primary
Base score
5.5
Impact score
3.6
Exploitability score
1.8
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Severity
MEDIUM

Weaknesses

nvd@nist.gov
NVD-CWE-noinfo

Social media

Hype score
Not currently trending

  1. Linux kernel: KTLS + sockmap "Reverse Order" Use-After-Free / Data Corruption https://t.co/RH5EmLQrji "CVE-2025-37756 has been hacked on google KernelCTF. This is a bypass for the CVE-2025-37756 patch, also can used for LPE with the same flow of CVE-2025-37756."

    @oss_security

    7 May 2026

    1969 Impressions

    1 Retweet

    21 Likes

    6 Bookmarks

    0 Replies

    0 Quotes

Configurations

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References

Sources include official advisories and independent security research.