CVE-2021-22890Public exploitNetwork attack vector

Traffic modification via proxy-origin session ticket confusion

Published Apr 1, 2021 · Updated Jun 9, 2025

Authentication bypass in curl 7.63.0 through 7.75.0 allows remote attackers controlling an HTTPS proxy to skip origin certificate checks. libcurl's TLS session cache failed to distinguish proxy and origin sessions, so a post-handshake TLS 1.3 ticket could resume the origin connection without its certificate check. Exploitation requires an OpenSSL-based build, TLS 1.3 to an HTTPS proxy, and a certificate accepted for the origin unless verification is disabled, enabling unnoticed traffic modification.

CVSS severity3.7
Low
EPSS probability3.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in curl 7.63.0 through 7.75.0 allows remote attackers controlling an HTTPS proxy to skip origin certificate checks. libcurl's TLS session cache failed to distinguish proxy and origin sessions, so a post-handshake TLS 1.3 ticket could resume the origin connection without its certificate check. Exploitation requires an OpenSSL-based build, TLS 1.3 to an HTTPS proxy, and a certificate accepted for the origin unless verification is disabled, enabling unnoticed traffic modification.

The record

CVE
CVE-2021-22890
Published
Apr 1, 2021
Updated
Jun 9, 2025
Vendor
curl
Product
curl
Classifications
CWE-300, CWE-290, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 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=7.63.0 to and including 7.75.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=7.63.0 to and including 7.75.0

Published CVSS scores

3.7NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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 exploitPublished

Weakness, pattern, technique

CWE-300Channel Accessible by Non-Endpoint
CWE-290Authentication Bypass by Spoofing
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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