Overview
CVE-2025-61729 describes a vulnerability found within the HostnameError.Error() function in the Go programming language. The vulnerability stems from the unbounded inclusion of hostnames within the error string construction, combined with the use of repeated string concatenation. This can lead to excessive resource consumption, potentially resulting in a Denial-of-Service (DoS) attack if a malicious actor provides a crafted certificate.
Technical Details
The core of the vulnerability lies in how the HostnameError.Error() function constructs its error message. Specifically, the function iterates through a list of hostnames without a limit and appends them to the error string. Moreover, the implementation uses repeated string concatenation, which in Go (prior to certain optimizations that may or may not be present in all versions) can have a quadratic runtime complexity (O(n^2)).
Therefore, an attacker could present a certificate containing a large number of invalid hostnames. When the HostnameError.Error() function is called to generate an error message related to this certificate, the excessive number of hostname appends and the quadratic string concatenation cause the application to consume significant CPU and memory resources, potentially leading to a DoS condition.
CVSS Analysis
CVSS Score: N/A
Severity: N/A
Rationale: The CVE currently lacks a CVSS score. The severity depends on the specific Go version and how heavily the HostnameError.Error() function is used in security-critical contexts. A CVSS score will likely be assigned as further analysis is conducted.
Possible Impact
The most likely impact of CVE-2025-61729 is a Denial-of-Service (DoS) attack. A malicious actor could exploit this vulnerability by:
- Presenting a crafted certificate with a large number of invalid hostnames.
- Triggering the
HostnameError.Error()function to be called during certificate validation. - Causing excessive resource consumption, leading to application unresponsiveness or crashes.
The severity of the impact will depend on the specific application and its resource limits. Systems with limited resources are more susceptible to this type of attack.
Mitigation or Patch Steps
The recommended mitigation is to update to a patched version of Go that addresses this vulnerability. The following resources indicate a fix has been implemented:
- Upgrade to a version of Go containing the fix described in Go Change List (CL) 725920.
- Refer to the Go security advisory golang-announce for official announcements and version details.
If upgrading is not immediately possible, consider implementing rate limiting or other resource management techniques to prevent a single attacker from consuming excessive resources.
