CVE-2023-1998 Spectre v2 SMT mitigations problem in Linux kernel
Attackers can exploit Spectre v2 side-channels to read sensitive memory from other threads when legacy IBRS is used without STIBP.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-1998?
CVE-2023-1998 is a medium-severity vulnerability in Debian Debian Linux, published on 21 Apr 2023. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
The Linux kernel allows userspace processes to enable mitigations by calling prctl with PR_SET_SPECULATION_CTRL which disables the speculation feature as well as by using seccomp. We had noticed that on VMs of at least one major cloud provider, the kernel still left the victim process exposed to attacks in some cases even after enabling the spectre-BTI mitigation with prctl. The same behavior can be observed on a bare-metal machine when forcing the mitigation to IBRS on boot command line.
This happened because when plain IBRS was enabled (not enhanced IBRS), the kernel had some logic that determined that STIBP was not needed. The IBRS bit implicitly protects against cross-thread branch target injection. However, with legacy IBRS, the IBRS bit was cleared on returning to userspace, due to performance reasons, which disabled the implicit STIBP and left userspace threads vulnerable to cross-thread branch target injection against which STIBP protects.
Which versions are affected by CVE-2023-1998?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2023-1998?
Apply the vendor's patch.
Is CVE-2023-1998 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-1998 exists.
Public exploit code: 1 Exploit-DB entry.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-26234, AZL-26368, DEBIAN-CVE-2023-1998, GHSA-mj4w-6495-6crx, UBUNTU-CVE-2023-1998.