CVE-2018-5735 in BIND
Summary
by MITRE
The Debian backport of the fix for CVE-2017-3137 leads to assertion failure in validator.c:1858; Affects Debian versions 9.9.5.dfsg-9+deb8u15; 9.9.5.dfsg-9+deb8u18; 9.10.3.dfsg.P4-12.3+deb9u5; 9.11.5.P4+dfsg-5.1 No ISC releases are affected. Other packages from other distributions who did similar backports for the fix for 2017-3137 may also be affected.
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Analysis
by VulDB Data Team • 02/10/2023
The vulnerability described in CVE-2018-5735 represents a critical assertion failure within the ISC BIND (Berkeley Internet Name Domain) software that emerged from an improper backport of a security fix for CVE-2017-3137. This issue specifically affects Debian distributions running version 9.9.5.dfsg-9+deb8u15, 9.9.5.dfsg-9+deb8u18, 9.10.3.dfsg.P4-12.3+deb9u5, and 9.11.5.P4+dfsg-5.1, creating a scenario where the software fails during validation operations due to an assertion that should never be triggered in normal operation. The root cause stems from the incorrect implementation of the fix for the previous vulnerability, which introduced a condition that causes the validator.c module to crash when processing certain malformed DNS responses.
This assertion failure occurs in the validator.c file at line 1858, where the software encounters a condition that violates an internal assumption about the state of DNS data structures during validation. The flaw manifests when the backported fix for CVE-2017-3137 incorrectly handles edge cases in DNS message processing, leading to a situation where the assertion mechanism that normally protects against programming errors triggers in legitimate operational scenarios. This creates a denial-of-service condition where DNS servers running the affected Debian packages become unresponsive when encountering specific malformed input patterns, effectively rendering them unable to process DNS queries until restarted.
The operational impact of this vulnerability extends beyond simple service disruption, as it creates a potential attack vector where malicious actors could exploit the assertion failure to cause continuous service interruptions against DNS infrastructure. The vulnerability affects systems that rely on BIND for authoritative or recursive DNS services, potentially impacting internet connectivity for end users and network services that depend on these DNS servers. The issue demonstrates the risks associated with backporting security fixes without thorough testing and validation, particularly when dealing with complex protocols like DNS where subtle implementation differences can lead to catastrophic failures. This vulnerability aligns with CWE-617, which addresses reachable assertions, and represents a classic example of how security patches can introduce new flaws when not properly validated in the target environment.
Organizations affected by this vulnerability should immediately implement mitigation strategies including upgrading to patched versions of ISC BIND, applying the proper security fixes from upstream, or implementing network-level protections that prevent malformed DNS responses from reaching the vulnerable systems. The recommended approach involves updating to Debian versions that contain the correct implementation of the CVE-2017-3137 fix, ensuring that the backport process properly validates all edge cases and maintains compatibility with the original fix. Additionally, system administrators should monitor for assertion failure logs and implement proper logging and alerting mechanisms to detect potential exploitation attempts. This vulnerability highlights the importance of maintaining proper version control and testing procedures when applying security patches, particularly in critical infrastructure components like DNS servers that form the backbone of internet connectivity. The incident also demonstrates the value of ATT&CK framework concepts related to privilege escalation and denial of service through software vulnerabilities, as the assertion failure could potentially be leveraged to gain further access to affected systems or disrupt critical network services.