CVE-2021-22926Public exploit

Client certificate substitution via ambiguous name lookup

Published Aug 5, 2021 · Updated May 28, 2026

Certificate-selection confusion in curl 7.33.0 through 7.77.0 allows local users to make libcurl send an attacker-chosen client certificate. With the macOS Secure Transport backend, CURLOPT_SSLCERT treats a matching file in the working directory as the certificate before checking the keychain name. The attack requires a shared writable current directory and a predictable certificate name; a planted file then replaces the intended identity in the TLS handshake.

CVSS severity7.5
High
EPSS probability9.82%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Certificate-selection confusion in curl 7.33.0 through 7.77.0 allows local users to make libcurl send an attacker-chosen client certificate. With the macOS Secure Transport backend, CURLOPT_SSLCERT treats a matching file in the working directory as the certificate before checking the keychain name. The attack requires a shared writable current directory and a predictable certificate name; a planted file then replaces the intended identity in the TLS handshake.

The record

CVE
CVE-2021-22926
Published
Aug 5, 2021
Updated
May 28, 2026
Vendor
curl
Product
curl
Classifications
CWE-295, T1036
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Aug 5, 2021CVE publishedPublication date reported by the CVE source.
  2. May 28, 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=curll 7.33.0 to and include 7.77.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

curl · curlversion=curll 7.33.0 to and include 7.77.0

Published CVSS scores

5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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.

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)
Vectorlocal
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1036Masquerading

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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