CVE-2021-39873Public exploitNetwork attack vector

User deception via spoofed OAuth error messages

Published Oct 4, 2021 · Updated Aug 4, 2024

Content spoofing in GitLab CE/EE before 14.1.7, 14.2 through 14.2.4, and 14.3.0 allows remote attackers to mislead users via OAuth callback errors. The GitHub and Bitbucket OAuth callback endpoints render the attacker-controlled error_description parameter as a visible sign-in error without constraining its message. Exploitation requires a user to open the crafted callback URL and trust the displayed text; the reported consequence is inducement to visit a malicious website.

CVSS severity4.3
Medium
EPSS probability0.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Content spoofing in GitLab CE/EE before 14.1.7, 14.2 through 14.2.4, and 14.3.0 allows remote attackers to mislead users via OAuth callback errors. The GitHub and Bitbucket OAuth callback endpoints render the attacker-controlled error_description parameter as a visible sign-in error without constraining its message. Exploitation requires a user to open the crafted callback URL and trust the displayed text; the reported consequence is inducement to visit a malicious website.

The record

CVE
CVE-2021-39873
Published
Oct 4, 2021
Updated
Aug 4, 2024
Vendor
GitLab
Product
GitLab
Classifications
T1566.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 4, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>=1.0, <14.1.7
  2. Affected versionversion=>=14.2, <14.2.5
  3. Affected versionversion=>=14.3, <14.3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

GitLab · GitLabversion=>=1.0, <14.1.7; version=>=14.2, <14.2.5; version=>=14.3, <14.3.1

Published CVSS scores

4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.3NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.3GitLabCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/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

T1566.002Spearphishing Link

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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