Coder AgentAPI exposed user chat history via a DNS rebinding attack

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

EPSS

• CVE-2025-59956: 0.43% estimated exploitation activity in the next 30 days; percentile 36.88 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary AgentAPI prior to version 0.4.0 was susceptible to a client-side DNS rebinding attack when hosted over plain HTTP on localhost. Impact An attacker could have gained access to the /messages endpoint served by the Agent API. This allowed for the unauthorized exfiltration of sensitive user data, specifically local message history, which could've included secret keys, file system contents, and intellectual property the user was working on locally. Remediation We've implemented an Origin and Host header validating middleware and set a secure by default configuration. Please upgrade to version 0.4.0 or later. Credits We'd like to thank Evan Harris from mcpsec.dev for reporting this issue and following the coordinated disclosure policy.

Published by the source

29 Sep 2025, 20:40 UTC

Last modified by the source

23 Oct 2025, 20:33 UTC

Source last checked

26 Oct 2026, 15:13 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-w64r-2g3w-w8w4

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# Patch Next advisory brief: CVE-2025-59956

Advisory: Coder AgentAPI exposed user chat history via a DNS rebinding attack
IDs: CVE-2025-59956, GHSA-w64r-2g3w-w8w4
Record: https://patchnext.com/advisories/cve-2025-59956 (revision 1, source checked 26 Oct 2026, 15:13 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/coder/agentapi 0.4.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/coder/agentapi: affected < 0.4.0; fixed in 0.4.0

## Suggested inspection (read-only)
- Go github.com/coder/agentapi: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/coder/agentapi.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w64r-2g3w-w8w4 (GitHub-reviewed advisory GHSA-w64r-2g3w-w8w4 lists affected ranges: Go github.com/coder/agentapi >=0 <0.4.0)

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