CVE-2021-38084Network attack vector

POP3 session command injection via uncleared STLS buffer

Published Aug 3, 2021 · Updated Aug 4, 2024

Command injection in Courier Mail Server before 1.1.5 allows man-in-the-middle attackers to inject POP3 commands across an STLS upgrade. The POP3 server leaves pipelined plaintext in its input buffer when STLS switches the connection to TLS, then processes those bytes inside the encrypted session. An attacker positioned on the client-server path can append commands to the STLS request and alter the authenticated session without knowing its credentials.

CVSS severity8.1
High
EPSS probability1.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Command injection in Courier Mail Server before 1.1.5 allows man-in-the-middle attackers to inject POP3 commands across an STLS upgrade. The POP3 server leaves pipelined plaintext in its input buffer when STLS switches the connection to TLS, then processes those bytes inside the encrypted session. An attacker positioned on the client-server path can append commands to the STLS request and alter the authenticated session without knowing its credentials.

The record

CVE
CVE-2021-38084
Published
Aug 3, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-74, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 3, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.1NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('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

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Your stack

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