critical CVSS 9 EPSS 0.31%

CVE-2026-73208·Dovecot vulnerability

An attacker that holds a token intended for a different purpose can authenticate, because when an OAuth2 token response does not contain a scope claim, the audience claim is used in its place and checked against the configured required scopes. These are different concepts, and the audience claim does not describe what a token is allowed to do. A token that grants no relevant permissions can be accepted because its intended recipient value happens to match a configured scope name, granting access that should have been denied. It also hides an identity provider misconfiguration where scopes are not being issued at all. Ensure the identity provider issues a scope claim for all tokens used with Dovecot, and that configured scope names do not match audience values. Update to non-vulnerable version. No publicly available exploits are known.

Severity
critical
Software
Dovecot
Fixed in
1:2.4.1+dfsg1-6+deb13u7
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 0.31% — higher than 22% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2026-73208 scores 9 on CVSS, so a successful attack would be serious — but at 0.31%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

Until: 1:2.4.1+dfsg1-6+deb13u7

Fixed in: 1:2.4.1+dfsg1-6+deb13u7

How to fix this CVE

Update Dovecot to version 1:2.4.1+dfsg1-6+deb13u7 or later to remediate this OAuth2 token validation bypass vulnerability. The fix ensures that Dovecot correctly validates scope claims in OAuth2 tokens and does not fall back to audience claims as a substitute. Additionally, verify with your identity provider that scope claims are being issued for all tokens and that configured scope names do not overlap with audience values.

sudo dnf update dovecot

Defensia detects this vulnerability

How to check if you are affected

  1. Run `dovecot --version` to check your installed Dovecot version; vulnerable versions are prior to 1:2.4.1+dfsg1-6+deb13u7
  2. Check if OAuth2 authentication is enabled in Dovecot by reviewing `/etc/dovecot/conf.d/` for oauth2 passdb configuration blocks
  3. Search Dovecot logs with `grep -i 'oauth2\|scope\|audience' /var/log/dovecot/*.log` for token validation events or mismatches between scope and audience claims
  4. After patching, run `dovecot --version` again to confirm the updated version is active and restart the service with `sudo systemctl restart dovecot`

FAQ

What is CVE-2026-73208?

This vulnerability allows attackers with a valid OAuth2 token for one purpose to authenticate as if they had authorization for a different purpose. Dovecot incorrectly uses the audience claim as a fallback when scope claims are missing, which can grant unintended access if the audience value happens to match a configured scope name.

Is CVE-2026-73208 being actively exploited?

No, there are currently no known public exploits or active exploitation in the wild, though the vulnerability is critical and should be patched immediately.

What versions of Dovecot are affected by CVE-2026-73208?

All versions prior to 1:2.4.1+dfsg1-6+deb13u7 are affected. This includes Dovecot 2.4.1 and earlier versions on Debian 13.

How do I check if my server is vulnerable to CVE-2026-73208?

Run `dovecot --version` and compare the output against 1:2.4.1+dfsg1-6+deb13u7; if your version is lower and OAuth2 authentication is enabled in your Dovecot configuration, your server is vulnerable.

Does Defensia detect CVE-2026-73208?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Dovecot is installed on a monitored server, CVE-2026-73208 will appear in your dashboard with remediation steps.

Related Dovecot CVEs

CVE-2026-40018CVSS 9None None None No publicly available exploits are known.
CVE-2026-33605CVSS 9An unauthenticated attacker can crash the ManageSieve login process by sending a small malformed command before authenticating. If running in high-security mode (default for community releases), only the attacker's own connection is terminated. If running in high-performance mode (default for Pro releases), all connections handled by the same managesieve-login process are terminated. Repeating the attack can cause denial of service for Sieve script management. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-40019CVSS 9An unauthenticated attacker can send a truncated quoted argument to the ManageSieve login process, which makes it spin in an infinite loop consuming CPU. This can cause degradation or denial of service for Sieve script management, and repeated connections can consume all available CPU on the server. Monitor system for abnormal CPU usage and kill the offending process. Restrict network access to the ManageSieve service to trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-27852CVSS 9An attacker that can send mail to a user can craft a message whose headers contain a very large number of email addresses or MIME parameters, which causes excessive memory usage when the message is later parsed. The message is still delivered, but reading it over IMAP can exhaust the memory limit of the process and terminate it, causing denial of service for the affected user. Update to non-vulnerable version. No publicly available exploits are known.
CVE-2026-42391CVSS 9An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

References

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