CVE-2020-37248Network attack vector

Credential disclosure via skipped STARTTLS enforcement

Published Jun 8, 2026 · Updated Jun 8, 2026

STARTTLS stripping in OfflineIMAP before 8.0.3 allows man-in-the-middle attackers to capture IMAP account credentials in cleartext. The __start_tls method in offlineimap/imapserver.py silently returns without issuing STARTTLS when the server capability list omits STARTTLS. An attacker must control the network path and remove that capability before authentication; configured STARTTLS then leaves the session unencrypted.

CVSS severity6.5
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

STARTTLS stripping in OfflineIMAP before 8.0.3 allows man-in-the-middle attackers to capture IMAP account credentials in cleartext. The __start_tls method in offlineimap/imapserver.py silently returns without issuing STARTTLS when the server capability list omits STARTTLS. An attacker must control the network path and remove that capability before authentication; configured STARTTLS then leaves the session unencrypted.

The record

CVE
CVE-2020-37248
Published
Jun 8, 2026
Updated
Jun 8, 2026
Vendor
OfflineIMAP
Product
OfflineIMAP
Classifications
CWE-348, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=0 <8.0.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OfflineIMAP · OfflineIMAPversion=0 <8.0.3

Published CVSS scores

6.5MITRECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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.

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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-348Use of Less Trusted Source
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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