CVE-2025-39946 tls: make sure to abort the stream if headers are bogus

Critical 9.8 Published 4 Oct 2025 Updated 5 Aug 2026

A flaw in the Linux kernel TLS implementation allows remote attackers to cause a denial of service via crafted network packets that trigger an integer overflow in socket buffer handling.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2025-39946?

CVE-2025-39946 is a critical vulnerability in Linux kernel, published on 4 Oct 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

tls: make sure to abort the stream if headers are bogus

Normally we wait for the socket to buffer up the whole record before we service it. If the socket has a tiny buffer, however, we read out the data sooner, to prevent connection stalls. Make sure that we abort the connection when we find out late that the record is actually invalid. Retrying the parsing is fine in itself but since we copy some more data each time before we parse we can overflow the allocated skb space.

Constructing a scenario in which we're under pressure without enough data in the socket to parse the length upfront is quite hard. syzbot figured out a way to do this by serving us the header in small OOB sends, and then filling in the recvbuf with a large normal send.

Make sure that tls_rx_msg_size() aborts strp, if we reach an invalid record there's really no way to recover.

Which versions are affected by CVE-2025-39946?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-39946?

Apply the vendor's patch.

Is CVE-2025-39946 being exploited?

There is no known exploitation of CVE-2025-39946 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

All Linux kernel vulnerabilities

Sources

Also known as A-432728472, A-446648770, ASB-A-432728472, ASB-A-446648770, AZL-68141, BELL-CVE-2025-39946 and 6 more.