CVE-2023-6516
📋 TL;DR
This vulnerability in BIND 9 DNS resolver allows attackers to cause uncontrolled memory growth by triggering specific query patterns that overwhelm cache cleanup mechanisms. Affected systems running BIND 9 as a recursive resolver may experience memory exhaustion leading to denial of service. This impacts BIND 9 versions 9.16.0 through 9.16.45 and 9.16.8-S1 through 9.16.45-S1.
💻 Affected Systems
- ISC BIND 9
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete DNS service outage due to memory exhaustion, causing recursive resolver failure and disrupting all DNS resolution for dependent systems.
Likely Case
Gradual performance degradation leading to intermittent DNS resolution failures and increased latency as memory consumption grows.
If Mitigated
Controlled memory growth with monitoring alerts, allowing for intervention before service disruption occurs.
🎯 Exploit Status
Exploitation requires sending specific query patterns to trigger the cache cleanup mechanism, but exact exploit details are not publicly documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: BIND 9.16.46 and 9.16.46-S1
Vendor Advisory: https://kb.isc.org/docs/cve-2023-6516
Restart Required: Yes
Instructions:
1. Download BIND 9.16.46 or later from ISC website. 2. Stop the named service. 3. Install the updated version. 4. Restart the named service. 5. Verify the new version is running.
🔧 Temporary Workarounds
Limit recursive queries
allRestrict recursive queries to trusted networks only to reduce attack surface
# In named.conf, add: allow-recursion { trusted_nets; }
Reduce max-cache-size
allLower the maximum cache size to limit potential memory growth
# In named.conf, add: max-cache-size 90%;
🧯 If You Can't Patch
- Implement strict network ACLs to limit DNS queries to trusted sources only
- Deploy memory monitoring with automated alerts for abnormal named process growth
🔍 How to Verify
Check if Vulnerable:
Check BIND version with: named -vCheck Version:
named -vVerify Fix Applied:
Verify version is 9.16.46 or later with: named -v📡 Detection & Monitoring
Log Indicators:
- Unusual memory growth in named process
- Increased cache cleanup activity
- Performance degradation logs
Network Indicators:
- Unusual query patterns from single sources
- Increased DNS query volume with specific patterns
SIEM Query:
process_name="named" AND memory_usage > threshold AND time_range=last_24h🔗 References
- http://www.openwall.com/lists/oss-security/2024/02/13/1
- https://kb.isc.org/docs/cve-2023-6516
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PNNHZSZPG2E7NBMBNYPGHCFI4V4XRWNQ/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ZDZFMEKQTZ4L7RY46FCENWFB5MDT263R/
- https://security.netapp.com/advisory/ntap-20240503-0008/
- http://www.openwall.com/lists/oss-security/2024/02/13/1
- https://kb.isc.org/docs/cve-2023-6516
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PNNHZSZPG2E7NBMBNYPGHCFI4V4XRWNQ/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ZDZFMEKQTZ4L7RY46FCENWFB5MDT263R/
- https://security.netapp.com/advisory/ntap-20240503-0008/
