CVE-2025-61729: Excessive Resource Consumption in Go's stdlib crypto/x509 Package
Summary
CVE-2025-61729: Within HostnameError.Error(), when constructing an error string, there is no limit to the number of hosts that will be printed out. Affects stdlib across 2 version ranges.
< 1.24.11
>= 1.25.0, < 1.25.5
Fixed in 1.24.11 or 1.25.5, depending on the release line you run. How to fix ↓
Also tracked for
The same CVE-2025-61729 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
The Go programming language's standard library (stdlib) includes a package called crypto/x509, which is responsible for handling X.509 certificates. These certificates are widely used for secure communications over networks. The package provides functionalities for parsing, validating, and managing certificates. However, it has a vulnerability that can lead to excessive resource consumption when handling error strings during host certificate validation.
Vulnerability Detail
The vulnerability arises within the HostnameError.Error() method, where there is no limit to the number of hosts printed in the error string. This can lead to a situation where a certificate from a malicious actor causes the application to consume excessive resources due to repeated string concatenation, resulting in quadratic runtime complexity. This can potentially lead to denial of service (DoS) conditions, affecting the performance and availability of applications relying on this package.
How To Fix
Latest published version: go1.25.5 as of 22 Oct 2026
go get stdlib@vgo1.25.5Upgrading to it may include breaking changes; the versions below are the minimum fixed release for this vulnerability.
If you can't move to the latest
The minimum fixed version depends on the release line you run.
-
< 1.24.111.24.11go get stdlib@v1.24.11 -
>= 1.25.0, < 1.25.51.25.5go get stdlib@v1.25.5
Tip — Not sure which release line you're on? Vulert can find the fix for the version you are using. Scan free →
Workaround
Currently, there are no specific workarounds mentioned for this vulnerability. However, it is advisable to validate and sanitize input certificates to mitigate potential risks until the package is updated.
Conclusion
CVE-2025-61729 represents a significant vulnerability in the Go standard library's crypto/x509 package, leading to excessive resource consumption. It is crucial for developers to update to the patched versions to protect their applications from potential denial of service attacks. Regular monitoring of dependencies using tools like Vulert can help maintain security.
See every vulnerability recorded for stdlib →
FAQ
CVE-2025-61729 is a vulnerability in the Go standard library's crypto/x509 package that can lead to excessive resource consumption when printing error strings for host certificate validation.
If your application uses the affected version of the crypto/x509 package, it may be susceptible to denial of service attacks due to excessive resource consumption when processing certain certificates.
The vulnerability affects Go versions prior to 1.24.11 and 1.25.5. Ensure you are using one of the patched versions to avoid this issue.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
While there are no specific workarounds, consider validating and sanitizing input certificates to reduce the risk of exploitation until you can update to a patched version.
References
Related vulnerabilities
Recent vulnerabilities recorded for stdlib.
