CVE-2021-22946Public exploitNetwork attack vector

Cleartext data exposure via skipped TLS enforcement

Published Sep 29, 2021 · Updated Apr 16, 2026

TLS enforcement bypass in curl 7.20.0 through 7.78.0 allows remote attackers to expose cleartext data through crafted server replies. The FTP state machine accepts a 230 greeting as authenticated, while IMAP and POP3 capability-error paths begin authentication without enforcing the requested TLS upgrade. Exposure requires an IMAP, POP3, or FTP transfer configured with --ssl-reqd or the equivalent libcurl setting and lets the responding server or an on-path attacker read unencrypted credentials or content.

CVSS severity7.5
High
EPSS probability4.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

TLS enforcement bypass in curl 7.20.0 through 7.78.0 allows remote attackers to expose cleartext data through crafted server replies. The FTP state machine accepts a 230 greeting as authenticated, while IMAP and POP3 capability-error paths begin authentication without enforcing the requested TLS upgrade. Exposure requires an IMAP, POP3, or FTP transfer configured with --ssl-reqd or the equivalent libcurl setting and lets the responding server or an on-path attacker read unencrypted credentials or content.

The record

CVE
CVE-2021-22946
Published
Sep 29, 2021
Updated
Apr 16, 2026
Vendor
curl
Product
curl
Classifications
CWE-325, CWE-319, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Apr 16, 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=curl 7.20.0 to and including 7.78.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=curl 7.20.0 to and including 7.78.0

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-325Missing Cryptographic Step
CWE-319Cleartext Transmission of Sensitive Information
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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