CVE-2026-125331: HarnessRouter reroute provider connections

Summary

HarnessRouter, a self-hosted unified API for running agent harnesses, is affected in multi-organization deployments where a console not in self-hosted mode is used. A remote attacker without logging in can use a made-up bearer token to rewrite another organization's provider connection to an attacker-controlled endpoint, so later prompts can be disclosed and attacker responses can influence tasks.

Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.

Read the original description

HarnessRouter is a self-hosted unified API for running agent harnesses with sessions, streaming, files, cancellation, and failure handling. Prior to 0.31.8, a console that is not in self-hosted mode attaches the server's internal key to requests carrying an Authorization header before validating the bearer, while the service-only PUT and GET /v1/orgs/{org}/connections/{name}, PUT /v1/orgs/{org}/policy/{backend}, and /internal/* routes trust that key and take the organization from the URL. In a multi-organization deployment, a remote caller can use a made-up bearer to rewrite another organization's provider connection to an attacker-controlled endpoint, causing later prompts to be disclosed and attacker-controlled responses to influence tasks. This issue is fixed in version 0.31.8.

cve.now Index

26Pcve.now Index 26 of 100 · methodology v3 · provisional

Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
Reach?/20Unknown. No tracked technology or package matched
Severity9.1/10CVSS 9.1
No patch0/5No signal

What would change the score

Would score about 71 if added to CISA KEV
Would score about 66 if CISA's SSVC rates exploitation active
Would score about 31 if advisories confirm default setups are exposed

How the score works · Rankings

What to do

Upgrade to a fixed version: 0.31.8.

Check your systems with an agent

Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.

Check whether my systems are affected by CVE-2026-125331 (HarnessRouter: Service-only routes that write an organization's provider connections could be reached through a multi-tenant console with…), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-125331 (entry last updated 2026-11-10):
Affected:
- HarnessRouter harnessrouter: fixed in 0.31.8
Fixed versions: 0.31.8.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-125331 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-125331 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/HarnessRouter/harnessrouter/security/advisories/GHSA-p6cq-54cg-8mpv
- https://github.com/HarnessRouter/harnessrouter/pull/418
- https://github.com/HarnessRouter/harnessrouter/commit/28609ec65ed671112d7e5418926bbd3cb3b25c00
- https://github.com/HarnessRouter/harnessrouter/releases/tag/v0.31.8
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Entry: https://cve.now/CVE-2026-125331
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-125331.

Timeline

Nov 10, 2026, 6:38 PM UTCCVE published
Nov 10, 2026, 8:54 PM UTCFirst seen by cve.now
Nov 10, 2026, 9:35 PM UTCPosted on X by cve.now

Affected versions

HarnessRouter harnessrouter
fixed in 0.31.8

Evidence 6

Vendor advisory · 1

Establishes: Affected and fixed versions.

Advisory
GitHub · HarnessRouter/harnessrouter · Advisory GHSA-p6cq-54cg-8mpv

CVE record · 2

Establishes: The identifier and description.

Record
CVE List · CVE-2026-125331
Record
NVD · CVE-2026-125331

Corrections

None so far.

Something wrong on this page? Report an error. Every fix is listed here.

Questions about CVE-2026-125331

Is CVE-2026-125331 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data

Which versions are affected by CVE-2026-125331?

harnessrouter: before 0.31.8.Source: cve.now feed data

How do I fix CVE-2026-125331?

Upgrade to a fixed version: 0.31.8.Source: cve.now feed data

HarnessRouter: Service-only routes that write an organization's provider connections could be reached through a multi-tenant console with…