CVE-2025-13878: BIND 9 DNS Server DoS Vulnerability

CVE-2025-13878 Overview

CVE-2025-13878 is a Denial of Service vulnerability affecting ISC BIND 9, the most widely deployed DNS server software. When the named daemon processes malformed BRID/HHIT resource records, it can trigger an unexpected termination, causing complete disruption of DNS services for affected systems.

This vulnerability allows remote attackers to crash DNS servers without authentication, potentially impacting all services that rely on DNS resolution within the affected infrastructure.

Critical Impact

Remote attackers can crash BIND 9 DNS servers by sending specially crafted BRID/HHIT records, causing denial of service for all dependent systems and services.

Affected Products

• BIND 9 versions 9.18.40 through 9.18.43
• BIND 9 versions 9.20.13 through 9.20.17
• BIND 9 versions 9.21.12 through 9.21.16
• BIND 9 versions 9.18.40-S1 through 9.18.43-S1 (Supported Preview Edition)
• BIND 9 versions 9.20.13-S1 through 9.20.17-S1 (Supported Preview Edition)

Discovery Timeline

• 2026-01-21 - CVE-2025-13878 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2025-13878

Vulnerability Analysis

This vulnerability is classified under CWE-617 (Reachable Assertion), which occurs when a program contains an assertion that can be triggered by an attacker. In this case, the BIND 9 named daemon fails to properly handle malformed BRID/HHIT resource records during DNS processing, resulting in an assertion failure that causes the daemon to terminate unexpectedly.

The vulnerability is exploitable over the network without requiring any authentication or user interaction. An attacker can craft malicious DNS queries or responses containing malformed BRID/HHIT records that, when processed by a vulnerable BIND server, trigger the assertion and crash the service. This represents a significant availability risk for organizations relying on affected BIND versions for DNS infrastructure.

Root Cause

The root cause of CVE-2025-13878 lies in insufficient validation of BRID/HHIT record data within the BIND 9 DNS processing code. When the named daemon encounters malformed records of these types, an internal assertion is triggered that was designed to catch programming errors but is instead reachable through crafted external input.

This assertion failure follows the CWE-617 pattern where defensive programming assertions become exploitable attack vectors when they can be triggered by external, untrusted data.

Attack Vector

The attack vector for this vulnerability is network-based. An attacker can exploit this vulnerability by:

1. Sending DNS queries that cause the target server to process or cache malformed BRID/HHIT records
2. Poisoning DNS responses with malformed BRID/HHIT records that are then processed by the vulnerable server
3. Operating a malicious authoritative DNS server that returns crafted responses to queries from the target

The vulnerability mechanism involves malformed BRID/HHIT DNS resource records that bypass initial parsing but trigger an assertion failure during subsequent processing. When the named daemon encounters these malformed records, the assertion check fails, causing the process to terminate immediately. This can be exploited remotely without authentication. For detailed technical information, refer to the ISC CVE-2025-13878 Documentation.

Detection Methods for CVE-2025-13878

Indicators of Compromise

• Unexpected termination of the named process with assertion failure messages in system logs
• DNS service outages correlated with unusual DNS query patterns
• Log entries containing references to BRID or HHIT record processing errors
• Repeated named crashes requiring service restarts

Detection Strategies

• Monitor system logs for named assertion failures and unexpected terminations
• Implement DNS query logging to identify unusual BRID/HHIT record queries
• Deploy network monitoring to detect anomalous DNS traffic patterns targeting your DNS infrastructure
• Use SentinelOne Singularity to monitor for process crashes and service disruptions on DNS servers

Monitoring Recommendations

• Configure alerts for named process crashes or unexpected restarts
• Implement log aggregation for DNS server logs to detect patterns of exploitation attempts
• Monitor DNS query rates and types for anomalies that may indicate attack reconnaissance
• Enable verbose logging on DNS servers during the patch transition period to capture potential exploitation attempts

How to Mitigate CVE-2025-13878

Immediate Actions Required

• Upgrade BIND 9 to patched versions: 9.18.44, 9.20.18, or 9.21.17 immediately
• For Supported Preview Edition users, upgrade to the corresponding S1 patched versions
• Implement DNS server redundancy to minimize service impact from potential attacks
• Consider temporarily restricting DNS query sources if immediate patching is not possible

Patch Information

ISC has released patched versions that address this vulnerability:

For complete technical details and additional guidance, refer to the ISC CVE-2025-13878 Documentation.

Workarounds

• Deploy DNS servers behind network firewalls that can filter malicious DNS traffic
• Implement rate limiting on DNS queries to reduce the impact of potential exploitation attempts
• Configure automatic restart policies for the named service to minimize downtime from crashes
• Consider deploying secondary DNS infrastructure using alternative DNS server software until patching is complete

# Example: Configure automatic restart for named service (systemd)
sudo systemctl edit named.service

# Add the following to the override file:
# [Service]
# Restart=always
# RestartSec=5

sudo systemctl daemon-reload
sudo systemctl restart named