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CVE Record

CVE-2021-32066: An issue was discovered in Ruby through 2.6.7, 2.7.x through 2.7.3, and 3.x through 3.0.1.

An issue was discovered in Ruby through 2.6.7, 2.7.x through 2.7.3, and 3.x through 3.0.1. Net::IMAP does not raise an exception when StartTLS fails with an an unknown response, which might allow man-in-the-middle attackers to bypass the TLS protections by leveraging a network position between the client and the registry to block the StartTLS command, aka a "StartTLS stripping attack."

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Ruby applications that use Net::IMAP could believe StartTLS protection was handled safely even when the upgrade failed with an unexpected response. A network-positioned attacker might strip StartTLS and expose IMAP traffic that was expected to be encrypted.

Executive priority

Treat as a targeted confidentiality risk, not a broad internet worm risk. Prioritize mail-handling Ruby systems, credential exposure paths, and environments where network interception is plausible.

Technical view

CVE-2021-32066 affects Ruby Net::IMAP in Ruby through 2.6.7, 2.7.x through 2.7.3, and 3.x through 3.0.1. Net::IMAP did not raise an exception for an unknown StartTLS failure response, enabling a potential StartTLS stripping bypass when an attacker can interfere with client-server traffic.

Likely exposure

Exposure is most likely in Ruby applications or services using Net::IMAP with StartTLS to connect to IMAP servers over untrusted or interceptable networks.

Exploitation context

The provided sources do not show CISA KEV listing or active exploitation. Practical abuse requires a man-in-the-middle network position and a client workflow that depends on Net::IMAP StartTLS protection.

Researcher notes

Evidence identifies a StartTLS stripping class flaw in Net::IMAP error handling. Source data lacks CVSS, CWE, and confirmed exploitation. Avoid assuming impact beyond Ruby Net::IMAP and downstream vendor packages listed in advisories.

Mitigation direction

  • Update Ruby or downstream Ruby packages according to vendor advisories.
  • Prioritize systems using Net::IMAP for mail access over untrusted networks.
  • Review Debian, Gentoo, Oracle, NetApp, and Ruby guidance for affected packaged versions.
  • Prefer configurations that require encrypted IMAP sessions and fail closed on TLS errors.

Validation and detection

  • Inventory Ruby runtimes and identify versions in the affected ranges.
  • Search code and dependencies for Net::IMAP StartTLS usage.
  • Confirm installed packages include vendor fixes from relevant advisories.
  • Check mail clients fail closed when TLS negotiation fails unexpectedly.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
9Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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