CVE-2025-31498
Remediation / Mitigation Strategy: CVE-2025-31498
Vulnerability Description: Use-after-free in the read_answers() function within the c-ares asynchronous resolver library. This occurs when process_answer() re-enqueues a query (due to DNS Cookie failure, lack of EDNS support, or TCP connection closure after response), and a subsequent failure to put the new transaction on the wire results in the connection handle being closed prematurely. read_answers() then attempts to access this closed handle, leading to a use-after-free condition.
Severity: High (CVSS Score: 8.3)
Known Exploit: While a remote attacker might be able to trigger this by flooding the target with ICMP UNREACHABLE packets (assuming control over the upstream nameserver), this scenario is untested. A local attacker might be able to trigger the issue by manipulating the system to cause send()/write() failures.
Remediation:
Upgrade c-ares: The primary and most effective remediation is to upgrade c-ares to version 1.34.5 or later. This version contains the fix for the use-after-free vulnerability.
Identify Affected Systems: Determine all systems within your infrastructure that utilize the c-ares library. This includes applications that directly link to c-ares, as well as any system services that rely on c-ares for DNS resolution.
Prioritize Patching: Prioritize patching systems exposed to external networks or those handling sensitive data, as these are at a higher risk of exploitation.
Testing: After upgrading c-ares, thoroughly test affected applications and services to ensure that the upgrade has not introduced any regressions and that DNS resolution is functioning correctly.
Mitigation (If immediate patching is not possible):
- Network Monitoring: Implement network monitoring to detect suspicious activity such as unusually high volumes of ICMP UNREACHABLE packets directed towards DNS servers.
- Limit External DNS Resolution: Restrict the scope of DNS resolution performed by vulnerable systems. If possible, use local DNS caches or forwarders to minimize direct interaction with potentially malicious external nameservers. This is a defense in depth approach and not a full solution.
- System Integrity Monitoring: Implement system integrity monitoring to detect unauthorized modifications to system files or configurations that could be used to facilitate a local attack.
- Rate Limiting: Implement rate limiting on DNS queries to prevent potential flooding attacks that might exacerbate the vulnerability.
- Disable DNS Cookies (Temporarily): Although not ideal, temporarily disabling DNS cookies might mitigate the re-enqueuing scenario if DNS Cookie failures are a common trigger. However, this will reduce DNS security. Evaluate the trade-off carefully.
Assigner
- GitHub, Inc. [email protected]
Date
- Published Date: 2025-04-08 14:15:35
- Updated Date: 2025-04-08 18:13:53