GHSA-22w5-2fxg-vrwx: Low severity go/github.com/opentofu/opentofu vulnerability
Impact
Unauthenticated denial of service.
Summary
When OpenTofu performs requests against an untrusted (or compromised) third-party server or connects to an attacker-controlled server, the initial connection negotiation can produce high CPU usage, leading to possible denial of service.
These vulnerabilities do not permit arbitrary code execution or allow disclosure of confidential information.
Details
OpenTofu relies on third-party implementations of TLS certificate verification and HTTP request execution from the standard library of the Go programming language.
The Go project has recently published the following advisories for those implementations which indirectly affect OpenTofu's behavior:
- CVE-2026-42504: Quadratic complexity in WordDecoder.DecodeHeader in mime - CVE-2026-27145: Inefficient candidate hostname parsing in crypto/x509
CVE-2026-42504 affects OpenTofu's K8S remote state implementation. The operator of a configuration that uses such a backend needs to double-check the trustworthiness of the server used for this purpose. In situations where the server is untrusted or compromised, an attacker could configure it to respond with an intentionally crafted HTTP response designed to target this specific vulnerability in the Go standard library, potentially leading to high CPU usage.
CVE-2026-27145 has a similar outcome: if an untrusted or compromised third-party server is used, an attacker could craft a specific TLS certificate that targets this vulnerability in the Go standard library, which could also lead to high CPU usage.
Typical use of OpenTofu already requires caution in selection of third-party dependencies.
Patches
OpenTofu v1.11.9 and v1.12.2 address these vulnerabilities by upgrading to the Go versions that fix them (v1.25.11 and v1.26.3).
The OpenTofu v1.10 series is also impacted by these vulnerabilities. However, that series is built with a version of Go for which no upstream fix is available. Adopting Go 1.25.11 for that series would effectively end support for certain versions of macOS and Linux, and the OpenTofu Project has determined that the impact of these vulnerabilities is not high enough to justify that disruption in a patch release. For those using OpenTofu v1.10 releases, we recommend planning an upgrade to OpenTofu v1.11.9 in the near future.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
go/github.com/opentofu/opentofuto a version that resolves this vulnerability.Fixed in 1.11.9 - Upgrade
Upgrade
go/github.com/opentofu/opentofuto a version that resolves this vulnerability.Fixed in 1.12.2 - Upgrade
Upgrade
opentofuto a version that resolves this vulnerability.Fixed in 1.11.9 - Upgrade
Upgrade
opentofuto a version that resolves this vulnerability.Fixed in 1.12.2 - Compensating control
For OpenTofu configurations that use the affected K8S remote state or any backend that makes requests to an untrusted (or compromised) third-party server, double-check the trustworthiness of the server used for this purpose; avoid attacker-controlled or compromised endpoints to reduce risk of CPU-exhaustion denial of service triggered by crafted TLS certificates/HTTP responses.
Event History
Frequently Asked Questions
Which OpenTofu deployments are most exposed?
Deployments that make requests to untrusted or compromised third-party servers, or connect to attacker-controlled servers, are exposed. The CVE-2026-42504 issue specifically affects OpenTofu configurations using the Kubernetes remote state backend.
What does an attacker need to control to trigger the issue?
The attacker needs to control, compromise, or otherwise cause OpenTofu to connect to a server involved in its request or connection negotiation. That server can induce high CPU consumption during the initial negotiation.
What is the practical impact if exploitation succeeds?
The stated impact is denial of service through high CPU usage. The issue does not allow arbitrary code execution or disclosure of confidential information.
What can operators do while assessing exposure?
Operators using the Kubernetes remote state backend should verify that the backend server is trustworthy. More generally, assess whether OpenTofu is configured to contact untrusted, compromised, or attacker-controlled third-party servers.