CVE-2020-15685Public exploitNetwork attack vector

Session tampering via undrained STARTTLS response buffer

Published Dec 22, 2022 · Updated Apr 16, 2025

IMAP response injection in Mozilla Thunderbird before 78.7 allows man-in-the-middle attackers to alter session behavior during STARTTLS. ProcessCurrentURL starts TLS without first clearing plaintext bytes already held in the IMAP socket and input buffers, so a forged response crosses the security boundary and is consumed as the answer to a later encrypted command. The attacker must control the IMAP server or network path and induce a STARTTLS connection; injected responses can spoof alerts or alter capability and login processing.

CVSS severity8.8
High
EPSS probability0.85%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

IMAP response injection in Mozilla Thunderbird before 78.7 allows man-in-the-middle attackers to alter session behavior during STARTTLS. ProcessCurrentURL starts TLS without first clearing plaintext bytes already held in the IMAP socket and input buffers, so a forged response crosses the security boundary and is consumed as the answer to a later encrypted command. The attacker must control the IMAP server or network path and induce a STARTTLS connection; injected responses can spoof alerts or alter capability and login processing.

The record

CVE
CVE-2020-15685
Published
Dec 22, 2022
Updated
Apr 16, 2025
Vendor
Mozilla
Product
Thunderbird
Classifications
CWE-77, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 22, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 16, 2025Record 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=unspecified <78.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Thunderbirdversion=unspecified <78.7

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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.

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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 exploitPublished

Weakness, pattern, technique

CWE-77Improper Neutralization of Special Elements used in a Command ('Command Injection')
T1557Adversary-in-the-Middle

Public exploit references

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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