CVE-2025-40775
📋 TL;DR
A vulnerability in BIND DNS servers causes immediate crash when processing DNS messages with TSIG containing invalid algorithm fields. This allows denial-of-service attacks against DNS infrastructure. Affects BIND 9 installations in specified version ranges.
💻 Affected Systems
- ISC BIND
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
DNS service becomes completely unavailable, disrupting all DNS resolution for dependent systems and services.
Likely Case
Targeted DNS servers crash and restart, causing temporary DNS outages until service restoration.
If Mitigated
Minimal impact with proper network segmentation and monitoring to detect and respond to crashes.
🎯 Exploit Status
Exploitation requires sending specially crafted DNS packets to vulnerable servers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: BIND 9.20.9 and 9.21.8
Vendor Advisory: https://kb.isc.org/docs/cve-2025-40775
Restart Required: Yes
Instructions:
1. Download patched version from ISC website. 2. Stop BIND service. 3. Install updated package. 4. Restart BIND service. 5. Verify service is running.
🔧 Temporary Workarounds
Restrict TSIG usage
allConfigure BIND to reject or ignore TSIG records if not required
Add 'allow-query { none; };' to TSIG keys in named.conf
Network filtering
linuxBlock external DNS queries with TSIG at network perimeter
iptables -A INPUT -p udp --dport 53 -m string --hex-string '|FF|' --algo bm -j DROP
🧯 If You Can't Patch
- Implement rate limiting on DNS queries to reduce attack impact
- Deploy redundant DNS servers with load balancing to maintain service during attacks
🔍 How to Verify
Check if Vulnerable:
Check BIND version with 'named -v' and compare against affected rangesCheck Version:
named -vVerify Fix Applied:
Verify installed version is 9.20.9+ or 9.21.8+ and test with simulated malicious packets📡 Detection & Monitoring
Log Indicators:
- BIND process crashes
- Assertion failure messages in logs
- High frequency of TSIG-related errors
Network Indicators:
- Spike in DNS queries with malformed TSIG
- Unusual source IPs sending DNS packets
SIEM Query:
source="bind" AND ("assertion failure" OR "TSIG" OR "abort")