CVE-2023-2911 Explained : Impact and Mitigation

This CVE record was assigned on May 26, 2023, and published on June 21, 2023, by the Internet Systems Consortium (ISC). The vulnerability is related to BIND 9, impacting versions 9.16.33 to 9.16.41, 9.18.7 to 9.18.15, 9.16.33-S1 to 9.16.41-S1, and 9.18.11-S1 to 9.18.15-S1.

Understanding CVE-2023-2911

The vulnerability in BIND 9 could allow an attacker to exploit a sequence of serve-stale-related lookups, leading to the unexpected termination of the "named" process due to a stack overflow.

What is CVE-2023-2911?

If the recursive-clients quota is exceeded on a BIND 9 resolver configured with specific parameters, it could result in "named" looping and terminating unexpectedly.

The Impact of CVE-2023-2911

An attacker can exploit this vulnerability by sending specific queries to the resolver, causing the "named" process to terminate unexpectedly.

Technical Details of CVE-2023-2911

The vulnerability arises when the

recursive-clients

quota is reached on a BIND 9 resolver configured with both

stale-answer-enable yes;

and

stale-answer-client-timeout 0;

.

Vulnerability Description

The issue stems from a sequence of serve-stale-related lookups, leading to a stack overflow and the unexpected termination of the "named" process.

Affected Systems and Versions

BIND 9 versions 9.16.33 through 9.16.41, 9.18.7 through 9.18.15, 9.16.33-S1 through 9.16.41-S1, and 9.18.11-S1 through 9.18.15-S1 are impacted by this vulnerability.

Exploitation Mechanism

By sending specific queries to the resolver, an attacker can exploit the vulnerability, causing the "named" process to terminate unexpectedly.

Mitigation and Prevention

To address CVE-2023-2911, several steps can be taken to mitigate the risk associated with this vulnerability.

Immediate Steps to Take

Setting the

stale-answer-client-timeout

parameter to

off

or a non-zero value can prevent the issue. Users of older versions who cannot upgrade should set

stale-answer-client-timeout

to

off

to avoid being vulnerable.

Long-Term Security Practices

While setting the

recursive-clients

limit to a high number can reduce the likelihood of exploitation, it is not recommended as this limit is crucial for preventing resource exhaustion.

Patching and Updates

Users are advised to upgrade to the patched release closest to their current BIND 9 version. The recommended releases to address this vulnerability are 9.16.42, 9.18.16, 9.16.42-S1, or 9.18.16-S1.