# CVE-2026-82756 — ash-project ash_authentication_oauth2_server

> As of 2026-09-08, CVE-2026-82756 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in ash-project ash_authentication_oauth2_server, CVSS v4.0 6.3, EPSS 0.3% (31.0th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-82756 as of 2026-09-08; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-09-08

## What is CVE-2026-82756?

Improper Encoding or Escaping of Output vulnerability in ash-project ash_authentication_oauth2_server allows an unauthenticated attacker to inject arbitrary authentication parameters into the WWW-Authenticate challenge header. BearerPlug and RequireScopePlug built the Bearer resource_metadata="..." challenge by interpolating a resource_metadata URL derived from the request tenant directly into the quoted value. In a multi-tenant application that sets the Ash tenant from request-controlled data (a subdomain, the Host, a path segment, or a header), a tenant containing a " closes the quoted value and appends attacker-chosen auth-params, including a second resource_metadata URL pointing at an attacker-controlled authorization server that spec-following clients follow. Carriage returns and line feeds are rejected by Plug, so this is parameter injection within one header, not response splitting. This issue affects ash_authentication_oauth2_server: from 0.1.3 before 0.3.1.

The record classifies CVE-2026-82756 under weakness class [CWE-116](https://intel.threadlinqs.com/cwe/CWE-116). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 28 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 6.3 — Medium (derived from score) (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N`)
- **EPSS (FIRST):** 0.3% probability of exploitation in the next 30 days, higher than 31.0% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-09-07, last modified 2026-09-08

## Is CVE-2026-82756 being exploited?

It currently carries a trending score of 38 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [ash-project](https://intel.threadlinqs.com/vendors/ash-project): ash_authentication_oauth2_server

## How to fix CVE-2026-82756

No vendor patch reference has been recorded for CVE-2026-82756 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-82756

No threat campaign in the Threadlinqs corpus currently references CVE-2026-82756, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-09-08. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com — vendor advisory](https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-2h3v-83jg-2qmm)
- [github.com — patch](https://github.com/ash-project/ash_authentication_oauth2_server/commit/09f97476715da031b136eaec7b2cda2363ad8149)

**Other references**

- [cna.erlef.org — related](https://cna.erlef.org/cves/CVE-2026-82756.html)
- [osv.dev — related](https://osv.dev/vulnerability/EEF-CVE-2026-82756)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-82756
Full detection coverage and IOCs for threats exploiting CVE-2026-82756 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp