CVE-2021-3491 Linux kernel io_uring PROVIDE_BUFFERS MAX_RW_COUNT bypass

What is CVE-2021-3491?

CVE-2021-3491 is a high-severity vulnerability in Canonical Ubuntu Linux, published on 4 Jun 2021. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

The io_uring subsystem in the Linux kernel allowed the MAX_RW_COUNT limit to be bypassed in the PROVIDE_BUFFERS operation, which led to negative values being usedin mem_rw when reading /proc/<PID>/mem. This could be used to create a heap overflow leading to arbitrary code execution in the kernel. It was addressed via commit d1f82808877b ("io_uring: truncate lengths larger than MAX_RW_COUNT on provide buffers") (v5.13-rc1) and backported to the stable kernels in v5.12.4, v5.11.21, and v5.10.37. It was introduced in ddf0322db79c ("io_uring: add IORING_OP_PROVIDE_BUFFERS") (v5.7-rc1).

Weakness: CWE-787, CWE-131

Which versions are affected by CVE-2021-3491?

It affects 2 products.

Products include Canonical Ubuntu Linux, Linux kernel.

How do I fix CVE-2021-3491?

Apply the vendor's patch.

Is CVE-2021-3491 being exploited?

There is no known exploitation of CVE-2021-3491 in the wild and no public exploit code.

Other vulnerabilities in Canonical Ubuntu Linux

• CVE-2020-11651 SaltStack Salt Authentication Bypass Exploited Critical 9.8
• CVE-2020-7247 OpenSMTPD Remote Code Execution Exploited Critical 9.8
• CVE-2019-16928 Exim Out-of-bounds Write Exploited Critical 9.8
• CVE-2018-6789 Exim Buffer Overflow Exploited Critical 9.8
• CVE-2015-2590 Oracle Java SE and Java SE Embedded Remote Code Execution Exploited Critical 9.8

All Canonical Ubuntu Linux vulnerabilities

Sources

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

Also known as A-190877100, DEBIAN-CVE-2021-3491, GHSA-q4c9-gg27-f3pq, PUB-A-190877100, UBUNTU-CVE-2021-3491.