CVE-2025-61729
📋 TL;DR
This vulnerability in Go's HostnameError.Error() function allows a malicious certificate to cause excessive resource consumption through unbounded string concatenation. It affects applications using Go's crypto/tls package for certificate validation. The quadratic runtime complexity can lead to denial of service conditions.
💻 Affected Systems
- Go programming language
- Applications using Go's crypto/tls package
📦 What is this software?
Go by Golang
Go by Golang
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service due to CPU/memory exhaustion, potentially crashing the application or making it unresponsive.
Likely Case
Degraded performance and increased resource usage when processing malicious certificates, leading to service disruption.
If Mitigated
Minimal impact with proper input validation and resource limits in place.
🎯 Exploit Status
Exploitation requires presenting a specially crafted certificate to a vulnerable TLS endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Go 1.23.3
Vendor Advisory: https://groups.google.com/g/golang-announce/c/8FJoBkPddm4
Restart Required: Yes
Instructions:
1. Update Go to version 1.23.3 or later. 2. Recompile all affected applications. 3. Restart services using the updated binaries.
🔧 Temporary Workarounds
Limit certificate SAN entries
allConfigure TLS endpoints to reject certificates with excessive Subject Alternative Name entries.
Implement rate limiting
allAdd rate limiting on TLS handshake attempts to mitigate DoS impact.
🧯 If You Can't Patch
- Implement network-level protections like WAF rules to block certificates with excessive SAN entries.
- Deploy resource limits (CPU, memory) on affected services to contain potential DoS impact.
🔍 How to Verify
Check if Vulnerable:
Check Go version with 'go version'. If output shows 1.23.0-1.23.2, the system is vulnerable.Check Version:
go versionVerify Fix Applied:
After updating, verify with 'go version' shows 1.23.3 or later.📡 Detection & Monitoring
Log Indicators:
- Unusually long error messages containing hostname lists
- Increased CPU/memory usage during TLS handshakes
- TLS handshake timeouts or failures
Network Indicators:
- TLS connections presenting certificates with many SAN entries
- Unusual volume of TLS handshake attempts
SIEM Query:
source="tls_logs" AND (message="*HostnameError*" OR message="*too many hostnames*")