CVE-2026-42791 (GCVE-0-2026-42791)
Vulnerability from cvelistv5 – Published: 2026-05-27 12:23 – Updated: 2026-07-24 14:14
VLAI
EPSS
VEX
Title
OCSP responder certificate validity period not checked in public_key
Summary
Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid.
OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid.
This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case — server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate.
This issue affects OTP from OTP 27.0 before OTP 29.0.1, OTP 28.5.0.1 and OTP 27.3.4.12, corresponding to public_key from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-05-27 15:40 UTC
CWE
Assigner
References
6 references
| URL | Tags |
|---|---|
| https://github.com/erlang/otp/security/advisories… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-42791.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-42791 | related |
| https://www.erlang.org/doc/system/versions.html#o… | x_version-scheme |
| https://github.com/erlang/otp/commit/7995f1fdaee3… | patch |
| https://github.com/erlang/otp/commit/b3870e02405c… | patch |
Impacted products
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"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "LOW",
"subIntegrityImpact": "LOW",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
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"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
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"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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{
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"role": "CISA Coordinator",
"timestamp": "2026-05-27T15:40:27.647844Z",
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"published": "2026-05-27T14:16:53.460",
"references": [
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{
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{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"tags": [
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"url": "https://osv.dev/vulnerability/EEF-CVE-2026-42791"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"tags": [
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"url": "https://www.erlang.org/doc/system/versions.html#order-of-versions"
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],
"sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"vulnStatus": "Modified",
"weaknesses": [
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"value": "CWE-295"
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{
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"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
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"redhat_vex": {
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"initial_release_date": "2026-05-27T12:23:13.584000+00:00",
"product_status:fixed": "79",
"product_status:known_not_affected": "42",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "erlang: Erlang OTP: Authentication bypass due to improper OCSP certificate validation",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42791.json",
"version": "3"
},
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-42791",
"options": [
{
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{
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{
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"role": "CISA Coordinator",
"timestamp": "2026-05-27T15:40:27.647844Z",
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{
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"modules": [
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"packageName": "public_key",
"packageURL": "pkg:otp/public_key?repository_url=https:%2F%2Fgithub.com%2Ferlang%2Fotp\u0026vcs_url=git%20https:%2F%2Fgithub.com%2Ferlang%2Fotp.git",
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"programRoutines": [
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"repo": "https://github.com/erlang/otp",
"vendor": "Erlang",
"versions": [
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"changes": [
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"status": "unaffected"
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{
"at": "1.20.3.1",
"status": "unaffected"
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{
"at": "1.21.1",
"status": "unaffected"
}
],
"lessThan": "*",
"status": "affected",
"version": "1.16",
"versionType": "otp"
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]
},
{
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"cpes": [
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"modules": [
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"repo": "https://github.com/erlang/otp",
"vendor": "Erlang",
"versions": [
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"status": "unaffected"
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"status": "affected",
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{
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"status": "unaffected"
},
{
"at": "b3870e02405c709a872b01ba6086065620cdfe76",
"status": "unaffected"
}
],
"lessThan": "*",
"status": "affected",
"version": "2b1a742c651b90f8a7a1fb2ddde73f29915ea376",
"versionType": "git"
}
]
}
],
"configurations": [
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"value": "For the \u003ctt\u003essl\u003c/tt\u003e application, OCSP stapling must be enabled by setting the \u003ctt\u003estapling\u003c/tt\u003e option to \u003ctt\u003estaple\u003c/tt\u003e in the TLS client options. OCSP stapling is not enabled by default.\u003cp\u003eApplications calling \u003ctt\u003epublic_key:pkix_ocsp_validate/5\u003c/tt\u003e directly are unconditionally affected when that function is used.\u003c/p\u003e"
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"value": "For the ssl application, OCSP stapling must be enabled by setting the stapling option to staple in the TLS client options. OCSP stapling is not enabled by default.\n\nApplications calling public_key:pkix_ocsp_validate/5 directly are unconditionally affected when that function is used."
}
],
"cpeApplicability": [
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"credits": [
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"lang": "en",
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],
"descriptions": [
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"lang": "en",
"supportingMedia": [
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"value": "Improper Certificate Validation vulnerability in Erlang OTP \u003ctt\u003epublic_key\u003c/tt\u003e (\u003ctt\u003epubkey_ocsp\u003c/tt\u003e module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid.\u003cp\u003eOCSP response verification in \u003ctt\u003epubkey_ocsp:verify_response/5\u003c/tt\u003e and \u003ctt\u003epubkey_ocsp:is_authorized_responder/3\u003c/tt\u003e in \u003ctt\u003elib/public_key/src/pubkey_ocsp.erl\u003c/tt\u003e does not check the validity period (\u003ctt\u003enotBefore\u003c/tt\u003e/\u003ctt\u003enotAfter\u003c/tt\u003e) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid.\u003c/p\u003e\u003cp\u003eThis affects TLS clients using OCSP stapling via the \u003ctt\u003essl\u003c/tt\u003e application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling \u003ctt\u003epublic_key:pkix_ocsp_validate/5\u003c/tt\u003e directly, where the impact depends on the use case \u2014 server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate.\u003c/p\u003e\u003cp\u003eThis issue affects OTP from OTP 27.0 before OTP\u0026nbsp;29.0.1, OTP\u0026nbsp;28.5.0.1 and OTP\u0026nbsp;27.3.4.12, corresponding to \u003ctt\u003epublic_key\u003c/tt\u003e from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.\u003c/p\u003e"
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"datePublished": "2026-05-27T12:23:13.584Z",
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}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.