CVE-2025-39946
tls: make sure to abort the stream if headers are bogus
CVSS 9.8 CRITICALEPSS 9.1%
In short
A flaw in Linux kernel's TLS implementation allows an attacker to cause a buffer overflow by sending malformed TLS record headers in small fragments followed by large data, potentially crashing the system or executing code.
Technical detail
The vulnerability exists in TLS record parsing when the kernel buffers incomplete records and attempts to recover by re-parsing with additional socket data. An attacker can exploit this by sending fragmented bogus headers followed by a large payload, causing the parser to overflow the allocated skb space when it retries parsing. The issue occurs because tls_rx_msg_size() fails to abort the stream parser (strp) upon detecting invalid records, allowing continued processing of corrupt data.
Summary generated and translated by AI from the 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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H