CVE-2026-27831
📋 TL;DR
CVE-2026-27831 is a heap-based out-of-bounds read vulnerability in rldns DNS server version 2.3 that can cause denial of service. The vulnerability allows attackers to crash the DNS server by reading memory beyond allocated heap boundaries. Organizations running rldns version 2.3 are affected.
💻 Affected Systems
- rldns DNS server
⚠️ 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
Complete DNS service disruption leading to inability to resolve domain names, potentially affecting all network services that rely on DNS.
Likely Case
DNS server crashes requiring manual restart, causing temporary service interruptions until recovery.
If Mitigated
Limited impact with proper monitoring and automated restart mechanisms in place.
🎯 Exploit Status
DNS protocol is unauthenticated by design, making exploitation straightforward. Public technical analysis and proof-of-concept details are available in the Medium article reference.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 1.4 (according to references, though CVE mentions version 2.3 vulnerability)
Vendor Advisory: https://github.com/bluedragonsecurity/rldns/security/advisories/GHSA-fv38-45j4-g9x4
Restart Required: Yes
Instructions:
1. Download rldns version 1.4 from official repository. 2. Stop the rldns service. 3. Replace the binary with the patched version. 4. Restart the rldns service. 5. Verify service is running correctly.
🔧 Temporary Workarounds
Network segmentation and access control
linuxRestrict network access to rldns servers to only trusted sources using firewall rules.
iptables -A INPUT -p udp --dport 53 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 53 -s trusted_network -j ACCEPT
iptables -A INPUT -p udp --dport 53 -j DROP
iptables -A INPUT -p tcp --dport 53 -j DROP
🧯 If You Can't Patch
- Implement rate limiting on DNS queries to reduce attack surface
- Deploy intrusion detection systems to monitor for abnormal DNS traffic patterns
🔍 How to Verify
Check if Vulnerable:
Check rldns version: rldns --version or examine installed package version. If version is 2.3, system is vulnerable.Check Version:
rldns --versionVerify Fix Applied:
After patching, verify version shows 1.4 or higher and test DNS resolution functionality.📡 Detection & Monitoring
Log Indicators:
- rldns process crashes or abnormal termination
- Core dumps in rldns working directory
- Increased error logs related to memory access
Network Indicators:
- Unusual volume of malformed DNS queries
- DNS resolution failures following specific query patterns
SIEM Query:
source="rldns.log" AND ("segmentation fault" OR "core dumped" OR "SIGSEGV")🔗 References
- https://github.com/bluedragonsecurity/rldns-1.3-heap-out-of-bounds-vulnerability-fixed-in-rldns-1.4
- https://github.com/bluedragonsecurity/rldns/security/advisories/GHSA-fv38-45j4-g9x4
- https://github.com/bluedragonsecurity/rldns_archives/blob/main/diff/rldns-1.4.diff
- https://medium.com/@w1sdom/heap-based-buffer-over-read-vulnerability-in-rldns-1-3-5da3bccdc031
- https://github.com/bluedragonsecurity/rldns/security/advisories/GHSA-fv38-45j4-g9x4
