CVE-2021-39185Public exploitNetwork attack vector

Credentialed response disclosure via reflected origins

Published Sep 1, 2021 · Updated Aug 4, 2024

Origin validation error in affected http4s CORS middleware releases allows remote attackers to read credentialed responses across origins. CORSConfig defaults anyOrigin and allowCredentials to true, so CORS reflects arbitrary origins, including null, while authorizing credentialed access. A victim browser must send a credentialed cross-origin request to an application using the default policy.

CVSS severity9.1
Critical
EPSS probability0.59%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation error in affected http4s CORS middleware releases allows remote attackers to read credentialed responses across origins. CORSConfig defaults anyOrigin and allowCredentials to true, so CORS reflects arbitrary origins, including null, while authorizing credentialed access. A victim browser must send a credentialed cross-origin request to an application using the default policy.

The record

CVE
CVE-2021-39185
Published
Sep 1, 2021
Updated
Aug 4, 2024
Vendor
http4s
Product
http4s
Classifications
CWE-346, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 1, 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=< 0.21.27
  2. Affected versionversion=>= 0.22.0, < 0.22.3
  3. Affected versionversion=>= 0.23.0, < 0.23.2
  4. Affected versionversion=>= 1.0.0-M1, <= 1.0.0-M24

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

http4s · http4sversion=< 0.21.27; version=>= 0.22.0, < 0.22.3; version=>= 0.23.0, < 0.23.2; version=>= 1.0.0-M1, <= 1.0.0-M24

Published CVSS scores

6.4NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:N
9.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-346Origin Validation Error
T1189Drive-by Compromise

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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