CVE-2021-37155Network attack vector

OCSP validation bypass via ignored serial mismatch

Published Jul 21, 2021 · Updated Aug 4, 2024

OCSP validation bypass in wolfSSL 4.6.0 through 4.7.x allows remote attackers to supply a response for a different certificate. CompareOcspReqResp reports a match when request and response serial numbers differ because the comparison error does not propagate as a verification failure. Exploitation requires OCSP to be enabled and permits a mismatched response to pass request-response matching, undermining certificate revocation checks.

CVSS severity9.8
Critical
EPSS probability1.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OCSP validation bypass in wolfSSL 4.6.0 through 4.7.x allows remote attackers to supply a response for a different certificate. CompareOcspReqResp reports a match when request and response serial numbers differ because the comparison error does not propagate as a verification failure. Exploitation requires OCSP to be enabled and permits a mismatched response to pass request-response matching, undermining certificate revocation checks.

The record

CVE
CVE-2021-37155
Published
Jul 21, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 21, 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

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

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 exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

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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