SmarterMail: Privilege escalation via stale JWT role claim in refresh token
Summary
SmarterMail embeds a role claim in JWT access and refresh tokens when they are issued, and does not check it against the account's current role when a refresh token is redeemed at POST /api/v1/auth/refresh-token. An attacker who holds a refresh token issued before an administrator was demoted, or a demoted user whose session was not updated, can obtain a new access token that keeps the higher role, such as DomainAdmin or SysAdmin, until the token expires. The attacker needs network access and a low-privilege account, according to the CVSS vector.
Affected
- SmarterMail versions before Build 9777
- Vendor data: affected 0 to < Build 9777
Fixed in
- Upgrade to SmarterMail Build 9777 (October 8, 2026) or later
- The vendor release notes list a fix that rejects login tokens of a domain administrator after the account is demoted. The notes do not reference the CVE ID, so this link is an inference.
Workaround
- Unknown. No vendor or third-party workaround was found in the sources.
- Until patched, limit administrator accounts and restrict access to the admin and API interface.
Exploitation
- CISA SSVC in the CVE record: exploitation none, automatable no, technical impact total.
- Not marked as known exploited in the sources reviewed.
- A public proof-of-concept repository covers this CVE together with CVE-2026-104082 and CVE-2026-104083, which describe a chain of issues.
Our recommendation
- Upgrade all SmarterMail instances to Build 9777 or later.
- Check whether any SmarterMail instance runs a build older than 9777.
- Review administrator and domain administrator accounts for recent demotions and revoke existing sessions where the product allows it.
- Ask administrators to log out and log in again after the upgrade.
- Limit the number of administrator accounts and avoid exposing the admin and API interface directly to the internet.
- Patch together with CVE-2026-104082 and CVE-2026-104083, which the sources describe as a chain.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- SmarterMail Release Notes (Build 9777) www.smartertools.com
- VulnCheck advisory: SmarterMail stale JWT role claim www.vulncheck.com
- Researcher write-up (blog.evan.lat) blog.evan.lat
- ACN bulletin on SmarterMail issues www.acn.gov.it
- HOL Guard CVE record for CVE-2026-104084 hol.org
- Rapid7 record via Vulners vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 05:07.
Original description (NVD)
SmarterMail before build 9777 contains a privilege escalation vulnerability where JWT access and refresh tokens embed a role claim at issuance that is not revalidated against the account's current role when redeemed through POST /api/v1/auth/refresh-token. Attackers who capture a refresh token issued before an administrator demotion, or a demoted user whose session was not actively polling at the time of demotion, can replay the stale token to obtain a new access token retaining the higher-privilege role (such as DomainAdmin or SysAdmin) until natural token expiry.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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