CVE-2026-42790 (GCVE-0-2026-42790)
Vulnerability from cvelistv5 – Published: 2026-05-27 15:09 – Updated: 2026-11-11 19:13
VLAI
EPSS
VEX
Title
nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification
Summary
Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_cert and public_key modules) allows a DNS nameConstraints bypass via subject CommonName fallback in TLS hostname verification.
Two flaws combine to allow a subordinate CA whose DNS nameConstraints are restricted (e.g. permitted;DNS:allowed.example.com) to issue a leaf certificate that an OTP TLS client accepts as a valid identity for an out-of-scope hostname (e.g. victim.example.com):
First, pubkey_cert:validate_names/6 in lib/public_key/src/pubkey_cert.erl only checks SAN DNS entries against nameConstraints. Per RFC 5280, a permitted DNS subtree only restricts certificates that contain a DNS-typed name. A leaf with no subjectAltName therefore trivially satisfies any permitted;DNS:... constraint regardless of its subject commonName.
Second, public_key:pkix_verify_hostname/3 in lib/public_key/src/public_key.erl falls back to the subject commonName when no subjectAltName is present, extracting id-at-commonName attributes as presented IDs and matching them against the reference hostname. The strict pkix_verify_hostname_match_fun(https) matcher does not suppress this fallback.
The result is that path validation accepts a CN-only leaf under a DNS-constrained intermediate (no SAN means the nameConstraints are not triggered), and hostname verification then accepts it via the CN fallback. The bypass is reachable from stock ssl:connect with verify_peer, a trusted CA, SNI, and the canonical strict https hostname matcher.
This issue affects OTP from OTP 19.3 before OTP 26.2.5.21, OTP 27.3.4.12, OTP 28.5.0.1, and OTP 29.0.1, corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-05-27 00:00 UTC
CWE
Assigner
References
13 references
| URL | Tags |
|---|---|
| https://github.com/erlang/otp/security/advisories… | vendor-advisoryrelated |
| https://cna.erlef.org/cves/CVE-2026-42790.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-42790 | related |
| https://www.erlang.org/doc/system/versions.html#o… | x_version-scheme |
| https://github.com/erlang/otp/commit/b0c245e8132b… | related |
| https://github.com/erlang/otp/commit/0769050c69d7… | patch |
| https://github.com/erlang/otp/commit/fb67c6d1836f… | patch |
| https://github.com/erlang/otp/commit/21abed64eb20… | patch |
| https://access.redhat.com/security/cve/CVE-2026-42790 | vdb-entryx_refsource_REDHAT |
| https://bugzilla.redhat.com/show_bug.cgi?id=2482286 | issue-trackingx_refsource_REDHAT |
| https://security.access.redhat.com/data/csaf/v2/v… | x_sadp-csaf-vex |
| https://access.redhat.com/errata/RHSA-2026:54757 | vendor-advisoryx_refsource_REDHAT |
| https://access.redhat.com/errata/RHSA-2026:39809 | vendor-advisoryx_refsource_REDHAT |
Impacted products
7 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Erlang | OTP |
Affected:
19.3 , < *
(otp)
cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:* |
||
| Erlang | OTP |
Affected:
1.4 , < *
(otp)
cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:* |
||
| Erlang | OTP |
Affected:
b0c245e8132bb13171e277b1af59c0cec00c9459 , < *
(git)
cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:* |
||
| Red Hat | Red Hat OpenStack Platform 16.2 |
Unaffected:
0:23.3.4.18-2.el8ost , < *
(rpm)
cpe:/a:redhat:openstack:16.2::el8 |
||
| Red Hat | Red Hat OpenStack Services on OpenShift 18.0 |
Unaffected:
0:26.2.5.21-2.el9ost , < *
(rpm)
cpe:/a:redhat:openstack:18.0::el9 |
||
| Red Hat | Red Hat Hardened Images |
cpe:/a:redhat:hummingbird:1
|
||
| Red Hat | Red Hat OpenStack Platform 17.1 |
cpe:/a:redhat:openstack:17.1
|
Date Public
2026-05-27 15:09
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"value": "Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_cert and public_key modules) allows a DNS nameConstraints bypass via subject CommonName fallback in TLS hostname verification.\n\nTwo flaws combine to allow a subordinate CA whose DNS nameConstraints are restricted (e.g. permitted;DNS:allowed.example.com) to issue a leaf certificate that an OTP TLS client accepts as a valid identity for an out-of-scope hostname (e.g. victim.example.com):\n\nFirst, pubkey_cert:validate_names/6 in lib/public_key/src/pubkey_cert.erl only checks SAN DNS entries against nameConstraints. Per RFC 5280, a permitted DNS subtree only restricts certificates that contain a DNS-typed name. A leaf with no subjectAltName therefore trivially satisfies any permitted;DNS:... constraint regardless of its subject commonName.\n\nSecond, public_key:pkix_verify_hostname/3 in lib/public_key/src/public_key.erl falls back to the subject commonName when no subjectAltName is present, extracting id-at-commonName attributes as presented IDs and matching them against the reference hostname. The strict pkix_verify_hostname_match_fun(https) matcher does not suppress this fallback.\n\nThe result is that path validation accepts a CN-only leaf under a DNS-constrained intermediate (no SAN means the nameConstraints are not triggered), and hostname verification then accepts it via the CN fallback. The bypass is reachable from stock ssl:connect with verify_peer, a trusted CA, SNI, and the canonical strict https hostname matcher.\n\nThis issue affects OTP from OTP\u00a019.3 before OTP\u00a026.2.5.21, OTP\u00a027.3.4.12, OTP\u00a028.5.0.1, and OTP\u00a029.0.1, corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1."
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"value": "\u003cp\u003eThe \u003ccode\u003everify_fun\u003c/code\u003e option in the \u003ccode\u003essl\u003c/code\u003e application can be used to ensure that TLS connections fail if the end-entity certificate is missing the \u003ccode\u003esubjectAltName\u003c/code\u003e extension or has no domain name. Do not use a \u003ccode\u003everify_fun\u003c/code\u003e that accepts the \u003ccode\u003ename_not_permitted\u003c/code\u003e error.\u003c/p\u003e"
},
{
"base64": false,
"type": "text/markdown",
"value": "The `verify_fun` option in the `ssl` application can be used to ensure that TLS connections fail if the end-entity certificate is missing the `subjectAltName` extension or has no domain name. Do not use a `verify_fun` that accepts the `name_not_permitted` error."
}
],
"value": "The verify_fun option in the ssl application can be used to ensure that TLS connections fail if the end-entity certificate is missing the subjectAltName extension or has no domain name. Do not use a verify_fun that accepts the name_not_permitted error."
}
]
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-42790",
"datePublished": "2026-05-27T15:09:01.860Z",
"dateReserved": "2026-04-29T18:06:33.251Z",
"dateUpdated": "2026-11-11T19:13:56.207Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
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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
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
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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.