CVE-2025-68259
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-12-16

Last updated on: 2025-12-18

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Don't skip unrelated instruction if INT3/INTO is replaced When re-injecting a soft interrupt from an INT3, INT0, or (select) INTn instruction, discard the exception and retry the instruction if the code stream is changed (e.g. by a different vCPU) between when the CPU executes the instruction and when KVM decodes the instruction to get the next RIP. As effectively predicted by commit 6ef88d6e36c2 ("KVM: SVM: Re-inject INT3/INTO instead of retrying the instruction"), failure to verify that the correct INTn instruction was decoded can effectively clobber guest state due to decoding the wrong instruction and thus specifying the wrong next RIP. The bug most often manifests as "Oops: int3" panics on static branch checks in Linux guests. Enabling or disabling a static branch in Linux uses the kernel's "text poke" code patching mechanism. To modify code while other CPUs may be executing that code, Linux (temporarily) replaces the first byte of the original instruction with an int3 (opcode 0xcc), then patches in the new code stream except for the first byte, and finally replaces the int3 with the first byte of the new code stream. If a CPU hits the int3, i.e. executes the code while it's being modified, then the guest kernel must look up the RIP to determine how to handle the #BP, e.g. by emulating the new instruction. If the RIP is incorrect, then this lookup fails and the guest kernel panics. The bug reproduces almost instantly by hacking the guest kernel to repeatedly check a static branch[1] while running a drgn script[2] on the host to constantly swap out the memory containing the guest's TSS. [1]: https://gist.github.com/osandov/44d17c51c28c0ac998ea0334edf90b5a [2]: https://gist.github.com/osandov/10e45e45afa29b11e0c7209247afc00b
CVSS Scores
EPSS Scores
Probability:
Percentile:
Meta Information
Published
2025-12-16
Last Modified
2025-12-18
Generated
2026-05-07
AI Q&A
2025-12-16
EPSS Evaluated
2026-05-05
NVD
CVE-2025-68259
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
Helpful Resources
Exploitability
CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability in the Linux kernel's KVM (Kernel-based Virtual Machine) SVM (Secure Virtual Machine) feature involves improper handling of certain interrupt instructions (INT3, INTO, or select INTn) during code patching. When the guest kernel modifies code using a mechanism that temporarily replaces the first byte of an instruction with an INT3 opcode, the KVM must correctly decode and re-inject the interrupt. If the code changes between execution and decoding, KVM may decode the wrong instruction and specify an incorrect next instruction pointer (RIP), leading to guest kernel panics (crashes) due to failed instruction lookups.


How can this vulnerability impact me? :

This vulnerability can cause the guest Linux kernel running inside a virtual machine to panic (crash) unexpectedly, especially during operations that modify code while it is being executed by other CPUs. This can lead to instability and potential denial of service within virtualized environments using KVM with SVM support.


How can this vulnerability be detected on my network or system? Can you suggest some commands?

This vulnerability most often manifests as "Oops: int3" panics on static branch checks in Linux guests. Detection can involve monitoring for such kernel panics related to int3 exceptions. Additionally, reproducing the bug involves running a script that repeatedly checks a static branch in the guest kernel while manipulating the guest's TSS memory from the host using a drgn script. Specific commands are not provided, but the referenced scripts for reproducing the bug are available at https://gist.github.com/osandov/44d17c51c28c0ac998ea0334edf90b5a and https://gist.github.com/osandov/10e45e45afa29b11e0c7209247afc00b which can be adapted for detection purposes.


What immediate steps should I take to mitigate this vulnerability?

The vulnerability has been resolved in the Linux kernel by ensuring that when re-injecting a soft interrupt from an INT3, INT0, or select INTn instruction, the exception is discarded and the instruction retried if the code stream has changed. Immediate mitigation would involve updating the Linux kernel to a version that includes this fix. No other specific mitigation steps or workarounds are provided.


Ask Our AI Assistant
Need more information? Ask your question to get an AI reply (Powered by our expertise)
0/70
EPSS Chart