Go Programming Language 1.26 Patches Several Security Flaws
The Go programming language team has issued security updates for Go 1.25.6 and Go 1.24.12 to address six vulnerabilities.
These issues range from denial-of-service attacks and memory exhaustion to toolchain flaws that could enable arbitrary code execution in certain developer environments.
The patched issues span core standard library components including archive/zip and net/http, as well as security-sensitive areas of the crypto/tls stack. Two of the most serious weaknesses affect the Go toolchain itself, where crafted inputs could lead to command execution when building or fetching dependencies under specific conditions.
The releases follow Go’s PRIVATE track security policy, a process used when vulnerabilities violate committed security properties and require coordination prior to disclosure. Under this model, fixes are delivered through scheduled minor releases rather than out-of-band patches, giving enterprises and downstream maintainers a clear upgrade path while still allowing time for responsible reporting and remediation.
Memory exhaustion and DoS issues highlight service exposure risk
Two of the six vulnerabilities involve memory exhaustion or computational exhaustion that attackers could exploit to knock systems offline. While these bugs do not directly grant unauthorized access, they can have significant impact in production settings where Go-based services handle untrusted input at scale.
The most severe denial-of-service vulnerability is tied to the archive/zip package. Tracked as CVE-2025-61728, the flaw stems from a super-linear file name indexing algorithm that triggers when opening files inside ZIP archives. In practical terms, attackers can craft malicious ZIP files engineered to consume disproportionate CPU resources during indexing. If a Go service automatically processes ZIP uploads or scans archives as part of workflows such as document ingestion, CI pipelines, malware scanning, or content extraction, the issue could be used to exhaust compute resources and disrupt availability.
Security researcher Jakub Ciolek discovered CVE-2025-61728, and the problem has been resolved in the newly released versions.
A second denial-of-service weakness, CVE-2025-61726, affects net/http’s Request parseForm function. The risk comes from how Go parses URL-encoded forms containing a very large number of key-value pairs. Under these conditions, the parser can allocate excessive memory, potentially leading to memory exhaustion and process instability or termination.
This vulnerability was reported by researcher jub0bs. The implications are especially important for internet-facing applications that accept large POST requests, process form submissions from untrusted sources, or expose endpoints that can be hit repeatedly by automated traffic. Even if upstream infrastructure includes rate limiting, an attacker may be able to trigger outsized memory pressure with fewer requests than expected, increasing the chance of service disruption.
TLS vulnerabilities affect session security assumptions
Three vulnerabilities patched in the crypto/tls module focus on session handling and handshake behavior, areas that can affect confidentiality, authentication strength, and the reliability of security guarantees in long-running applications.
CVE-2025-68121 addresses an issue where Config.Clone improperly copies automatically generated session ticket keys, potentially allowing unauthorized session resumption. Session tickets are designed to let clients resume previous TLS sessions efficiently, reducing connection overhead. If ticket key handling is flawed, attackers could potentially take advantage of unintended key reuse or sharing behaviors to resume sessions they should not have access to.
The same researcher, Coia Prant, also reported another server-side TLS issue where only the leaf certificate’s expiration was checked during session resumption, while expired intermediate or root certificates were not properly evaluated. In environments with strict certificate lifecycle controls, this type of gap can create confusing edge cases where sessions remain valid longer than intended, weakening policy enforcement and increasing exposure if trust chains are not being properly refreshed.
A third TLS-related vulnerability, CVE-2025-61730, is tied to encryption-level handling during handshakes. The flaw allowed handshake messages to be processed at incorrect encryption levels when multiple messages span encryption boundaries, potentially exposing information to attackers with network-local visibility. In real-world terms, the highest risk is likely in shared networks, corporate environments, or scenarios where attackers can observe and interact with traffic locally, rather than broad remote exploitation across the public internet.
Arbitrary code execution risks center on the toolchain
While denial-of-service bugs can disrupt services, the most serious business impact often comes from vulnerabilities that enable code execution, especially inside build systems. Two CVEs patched in this release affect cmd/go behavior, which plays a central role in module fetching, dependency resolution, and compilation.
CVE-2025-61731 involves CgoPkgConfig, where unsanitized compiler flags could allow pkg-config to be invoked with malicious parameters. Because pkg-config influences compiler and linker flags, improper sanitization can become a bridge into executing unintended commands or injecting dangerous options. This matters most for environments that rely heavily on cgo, use system libraries through pkg-config, or perform automated builds of untrusted or third-party code.
RyotaK from GMO Flatt Security identified this issue, describing it as a bypass of flag sanitization.
Another toolchain vulnerability, CVE-2025-68119, impacts Go’s VCS integration. On systems with Mercurial or Git installed, arbitrary code execution could occur when downloading modules from non-standard sources or building modules that include malicious version strings. This is particularly relevant for developer machines and CI runners, where module fetching happens frequently and often automatically.
In response, the toolchain now blocks version strings prefixed with “-” or “/” characters, closing a path that could be used to manipulate command-line behavior. This vulnerability was discovered by Splitline from the DEVCORE Research Team.
What organizations should do next
Go teams are being advised to upgrade to Go 1.25.6 or Go 1.24.12 as soon as practical, especially if they operate internet-facing Go services, process ZIP uploads, accept large URL-encoded form payloads, or run build environments that pull dependencies from external sources.
Even organizations that do not believe they are directly exposed may still be impacted indirectly. For example, services may consume archives or requests via internal integrations, while CI systems often build or test third-party modules as part of routine workflows. In those cases, denial-of-service vulnerabilities can become operational stability problems, and toolchain weaknesses can elevate supply-chain risk.
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