CVE-2021-46999 sctp: do asoc update earlier in sctp_sf_do_dupcook_a

What is CVE-2021-46999?

CVE-2021-46999 is a critical use after free vulnerability in Linux kernel, published on 28 Feb 2024. 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:

sctp: do asoc update earlier in sctp_sf_do_dupcook_a

There's a panic that occurs in a few of envs, the call trace is as below:

[] general protection fault, ... 0x29acd70f1000a: 0000 [#1] SMP PTI [] RIP: 0010:sctp_ulpevent_notify_peer_addr_change+0x4b/0x1fa [sctp] [] sctp_assoc_control_transport+0x1b9/0x210 [sctp] [] sctp_do_8_2_transport_strike.isra.16+0x15c/0x220 [sctp] [] sctp_cmd_interpreter.isra.21+0x1231/0x1a10 [sctp] [] sctp_do_sm+0xc3/0x2a0 [sctp] [] sctp_generate_timeout_event+0x81/0xf0 [sctp]

This is caused by a transport use-after-free issue. When processing a duplicate COOKIE-ECHO chunk in sctp_sf_do_dupcook_a(), both COOKIE-ACK and SHUTDOWN chunks are allocated with the transort from the new asoc. However, later in the sideeffect machine, the old asoc is used to send them out and old asoc's shutdown_last_sent_to is set to the transport that SHUTDOWN chunk attached to in sctp_cmd_setup_t2(), which actually belongs to the new asoc. After the new_asoc is freed and the old asoc T2 timeout, the old asoc's shutdown_last_sent_to that is already freed would be accessed in sctp_sf_t2_timer_expire().

Thanks Alexander and Jere for helping dig into this issue.

To fix it, this patch is to do the asoc update first, then allocate the COOKIE-ACK and SHUTDOWN chunks with the 'updated' old asoc. This would make more sense, as a chunk from an asoc shouldn't be sent out with another asoc. We had fixed quite a few issues caused by this.

Weakness: CWE-416

Which versions are affected by CVE-2021-46999?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2021-46999?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2021-46999 being exploited?

There is no known exploitation of CVE-2021-46999 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-46999, GHSA-c4xm-6jcf-xfq6, UBUNTU-CVE-2021-46999.