CVE-2021-33515Network attack vector

Credential and mail redirection via STARTTLS command injection

Published Jun 28, 2021 · Updated Aug 3, 2024

STARTTLS command injection in Dovecot 2.3.0 through 2.3.14 allows remote authenticated users in an on-path position to redirect credentials and mail. The submission service accepts plaintext SMTP commands before STARTTLS and executes them after TLS negotiation in the client session. Exploitation requires valid submission credentials and an on-path position, and the bounded impact is credential theft and redirection of email.

CVSS severity4.2
Medium
EPSS probability2.85%
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

STARTTLS command injection in Dovecot 2.3.0 through 2.3.14 allows remote authenticated users in an on-path position to redirect credentials and mail. The submission service accepts plaintext SMTP commands before STARTTLS and executes them after TLS negotiation in the client session. Exploitation requires valid submission credentials and an on-path position, and the bounded impact is credential theft and redirection of email.

The record

CVE
CVE-2021-33515
Published
Jun 28, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-74, CWE-77, T1557
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.8NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:N
4.2OX Software GmbHCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-74Failure to Sanitize Data into a Different Plane ('Injection')
CWE-77Improper Neutralization of Special Elements used in a Command ('Command Injection')
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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