A logical error has been discovered in XSA-407 (Branch Type Confusion). Due to this error, the intended mitigation is not applied correctly, making it vulnerable to potential attacks. XSA-434 (Speculative Return Stack Overflow) is equally affected by this error, as it utilizes the same infrastructure. This post aims to provide insight into the issue, code snippets to demonstrate the problem, and exploit details for better understanding.

Overview

XSA-407 (Branch Type Confusion) is an advisory addressing a Xen vulnerability that deals with type confusion between different branch instructions. XSA-434 (Speculative Return Stack Overflow) is an advisory highlighting a Xen vulnerability related to speculative execution that could cause a return stack overflow. The issue lies in the insufficient mitigation for both issues, as a result of the logical error in XSA-407.

For more in-depth information, please refer to the original references

- XSA-407 Advisory
- XSA-434 Advisory

To demonstrate the error in XSA-407, let's take a look at the problematic section of the code

switch (branch_type) {
case INDIRECT:
    mitigation = XEN_DOMCTL_BT_SPEC_CTRL_INDIRECT_THUNK;
    break;
case RETURN:
    /* Fallthrough intended */
case CALL:
    mitigation = XEN_DOMCTL_BT_SPEC_CTRL_RETURN_THUNK;
    break;
default:
    ASSERT_UNREACHABLE();
    break;
}

The issue here is that the "Fallthrough intended" comment is incorrect. It causes the mitigation for a 'RETURN' branch type to be incorrectly applied, rendering it ineffective.

Exploit Details

The error in the XSA-407 mitigation might be exploited by an attacker, leading to branch target injection attacks. Since XSA-434 also uses the same infrastructure, the exploit of this logical error may also affect its vulnerability as well. With proper knowledge and access to both the host and guest systems, an attacker might be able to compromise sensitive information and even control the systems on which the Xen hypervisor is deployed.

Conclusion

The logical error found in XSA-407 causes the incorrect application of the mitigation intended for the vulnerability. This error makes both XSA-407 and XSA-434 vulnerable to potential attacks, thus compromising the security of Xen hypervisor systems. It is crucial to identify such errors and fix them accordingly to ensure the safety and integrity of virtualized infrastructures.

In light of these findings, it is highly recommended that users and system administrators running Xen in their infrastructures keep their systems updated and apply the appropriate patches to address the vulnerabilities mentioned in this post. By staying informed and proactive about the potential issues that may arise, users can better protect their systems from possible exploits and attacks.

Timeline

Published on: 05/16/2024 14:15:08 UTC
Last modified on: 05/16/2024 15:44:44 UTC