CVE-2026-81036Public exploitNetwork attack vector

Mail account takeover via unvalidated OAuth redirect

Published Aug 26, 2026 · Updated Aug 26, 2026

Open redirect in Stalwart Mail Server 0.16.19 and earlier allows remote attackers to take over mail accounts via a crafted OAuth login URL. When client authentication is disabled by default, validate_client_registration returns success without matching redirect_uri to a registered destination, and the login page sends the authorization code to that URI. An account holder must open the crafted URL and authenticate; the attacker can then exchange the disclosed code for access and refresh tokens and read the account's mail.

CVSS severity8.5
High
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Open redirect in Stalwart Mail Server 0.16.19 and earlier allows remote attackers to take over mail accounts via a crafted OAuth login URL. When client authentication is disabled by default, validate_client_registration returns success without matching redirect_uri to a registered destination, and the login page sends the authorization code to that URI. An account holder must open the crafted URL and authenticate; the attacker can then exchange the disclosed code for access and refresh tokens and read the account's mail.

The record

CVE
CVE-2026-81036
Published
Aug 26, 2026
Updated
Aug 26, 2026
Vendor
Stalwart Labs
Product
Stalwart
Classifications
CWE-601, T1528
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=0.16.19

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Stalwart Labs · Stalwartversion=0 <=0.16.19

Published CVSS scores

8.5VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
8.1VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-601URL Redirection to Untrusted Site ('Open Redirect')
T1528Steal Application Access Token

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo