Reliance on Untrusted Inputs in a Security Decision Affecting github.com/temporalio/temporal/chasm/lib/callback package, versions >=1.30.0 <1.30.7>=1.31.0 <1.31.3
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-GOLANG-GITHUBCOMTEMPORALIOTEMPORALCHASMLIBCALLBACK-20074847
- published24 Sept 2026
- disclosed21 Sept 2026
Introduced: 21 Sep 2026
NewCVE-2026-87858 (opens in a new tab)How to fix?
Upgrade github.com/temporalio/temporal/chasm/lib/callback to version 1.30.7, 1.31.3 or higher.
Overview
Affected versions of this package are vulnerable to Reliance on Untrusted Inputs in a Security Decision through the Nexus callback routing logic in chasm/lib/callback/request.go and components/callbacks/request.go. An attacker can make the History service send a state-changing internal HTTP request as an administrator by supplying a callback URL that matches the allowed callback host and setting a non-empty source header on the callback request. The vulnerable routing path treats that caller-controlled header as proof that the callback is internal and rewrites the request to the local frontend client while preserving the attacker-chosen path, query, and body. In deployments with an internal frontend HTTP API enabled, this lets an authenticated namespace user trigger administrative actions such as terminating workflows, registering namespaces, changing namespace configuration, or deleting namespaces and their workflows in namespaces they do not control.