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Date: Mon, 28 Jun 2021 09:58:23 +0300 (EEST)
From: Aki Tuomi <>
To: "" <>
Subject: CVE-2021-29157: Dovecot oauth2 JWT local validation path traversal

Open-Xchange Security Advisory 2021-06-28

Affected product: Dovecot IMAP Server
Vendor: OX Software GmbH

Internal reference: DOP-2159 
Vulnerability type: Path Traversal (CWE-24)
Vulnerable version: 2.3.11
Vulnerable component: oauth2
Report confidence: Confirmed
Solution status: Fixed in 2.3.15
Researcher credits: Kirin of Tencent Security Xuanwu Lab.
Vendor notification: 2021-03-22
CVE reference: CVE-2021-29157
CVSS: 6.7 (CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N)

Vulnerability Details:
If attacker can gain access to local filesystem, it is possible to trick Dovecot to use attacker specified key to validate tokens.

Steps to reproduce:

Configure Dovecot to perform OAUTH2 authentication with local JWT validation using posix fs driver.

Place base64 encoded HS256 shared key in a location that is readable by dovecot, and use ../../../../../location/to/path as key azp. 

You can now forge tokens and authenticate as any valid user.

Attacker can gain access using forged credentials.

Upgrade to fixed version.

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