NVD / CVE Program· CNA EEF

CVE-2026-42789: Non-CA certificate accepted as intermediate issuer in public_key path validation

Noroxi assessment

Priority: Monitor (action score 28/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.38% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Erlang OTP 0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8, 1.17.1.7, 1.20.3.6; azl3 erlang 26.2.5.20-1 on Azure Linux 3.0 26.2.5.21-1.

Low priority for now. Upgrade to Erlang OTP 0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8, 1.17.1.7, 1.20.3.6; azl3 erlang 26.2.5.20-1 on Azure Linux 3.0 26.2.5.21-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery. In lib/public_key/src/pubkey_cert.erl, pubkey_cert:validate_extensions/7 contains two flaws that together allow a certificate with basicConstraints cA:false and no keyUsage extension to be used as an intermediate issuer in a chain passed to public_key:pkix_path_validation/3: the cA:false clause recurses into the remaining extensions without rejecting the certificate when it is in issuer position, and the keyUsage check only fires when the extension is present, so a certificate lacking keyUsage entirely bypasses the keyCertSign enforcement. Any party holding an end-entity certificate with basicConstraints cA:false and no keyUsage extension, issued by any CA in the victim's trust store, can use that certificate's private key to sign forged leaf certificates for arbitrary identities. public_key:pkix_path_validation/3 accepts the resulting chain, and by extension every TLS or mTLS endpoint built on the OTP ssl application that relies on the default verifier is affected, including server identity verification on the client side and client certificate verification on mTLS servers. This issue affects OTP from OTP 17.0 before OTP 27.3.4.19, OTP 28.5.0.8, and OTP 29.1.2, corresponding to public_key from 0.22 before 1.17.1.7, 1.20.3.6, and 1.21.8. Whether OTP before OTP 17.0, corresponding to public_key before 0.22, is affected is unknown.

HighCVSS 7.0 · v4.0—No exploit Fix available

Published: May 27, 2026
Updated: Oct 26, 2026
EPSS: 0.3% · 32th percentile
CWE: CWE-295

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 28 / 40 · 7.0 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · EEF: 7.0; NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:H/SI:H/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
erlang	erlang/otp	cpe:2.3:a:erlang:erlang/otp

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Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

erlang erlang/otp17.0 and later · before 26.2.5.21
erlang erlang/otp27.0 and later · before 27.3.4.12
erlang erlang/otp28.0 and later · before 28.5.0.1
erlang erlang/otp29.0 and later · before 29.0.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (EEF). Independent of NVD's CPE analysis and usually ahead of it.

Erlang OTP
- 17.0 and lateraffected · otpfixed in 27.3.4.19, 28.5.0.8, 29.1.2
- 0.22 and lateraffected · otpfixed in 1.17.1.7, 1.20.3.6, 1.21.8
- 84adefa331c4159d432d22840663c38f155cd4c1 and lateraffected · gitfixed in 0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8, 75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333, 82af606b5437c4de1276dbcc8855a47e88231226
- 0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8 and laternot affected · git
- 75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333 and laternot affected · git
- 82af606b5437c4de1276dbcc8855a47e88231226 and laternot affected · git

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	erlang	from 0	—
Debian:13	erlang	before 1:27.3.4.1+dfsg-1+deb13u3	1:27.3.4.1+dfsg-1+deb13u3
Debian:14	erlang	before 1:27.3.4.12+dfsg-1	1:27.3.4.12+dfsg-1
openSUSE:Leap 16.0	erlang	before 27.1.3-160000.5.1	27.1.3-160000.5.1
openSUSE:Tumbleweed	erlang	before 28.5.0.4-1.1	28.5.0.4-1.1
openSUSE:Tumbleweed	erlang27	before 27.1.3-2.1	27.1.3-2.1
Red Hat:hummingbird:1	erlang27	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-asn1	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-common_test	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-compiler	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-crypto	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-debugger	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-dialyzer	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-diameter	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-edoc	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-eldap	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-erl_interface	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-erts	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-et	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-eunit	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-examples	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-ftp	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-gdb-tools	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1
Red Hat:hummingbird:1	erlang27-inets	before 0:27.3.4.17-1.hum1	0:27.3.4.17-1.hum1

+54

Same product

erlang: all records

Other highest-scoring records for the same primary product.

CVE-2026-55953TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication
36Monitor
CVE-2026-49759Stack buffer overflow in SCTP error cause parsing in inet_drv allows remote VM crash
35Monitor
CVE-2026-59251Denial of service via exponential certificate policy tree growth in path validation
34Monitor

Published before and after this one in the same product

← EarlierCVE-2026-32144Apr 7, 2026 · OCSP designated-responder authorization bypass via missing signature verification
30Monitor
← EarlierCVE-2026-32147Apr 21, 2026 · SFTP chroot bypass via path traversal in SSH_FXP_FSETSTAT
21Monitor
Later →CVE-2026-42791May 27, 2026 · OCSP responder certificate validity period not checked in public_key
25Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Erlang OTP	0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8	Vendor (CNA)
Erlang OTP	1.17.1.7	Vendor (CNA)
Erlang OTP	1.20.3.6	Vendor (CNA)
Erlang OTP	1.21.8	Vendor (CNA)
Erlang OTP	27.3.4.19	Vendor (CNA)
Erlang OTP	28.5.0.8	Vendor (CNA)
Erlang OTP	29.1.2	Vendor (CNA)
Erlang OTP	75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333	Vendor (CNA)
Erlang OTP	82af606b5437c4de1276dbcc8855a47e88231226	Vendor (CNA)
azl3 erlang 26.2.5.20-1 on Azure Linux 3.0	26.2.5.21-1 · CBL-Mariner Releases	Microsoft (MSRC)
debian:erlang	1:27.3.4.1+dfsg-1+deb13u3 · Debian:13	Package registry (OSV)
opensuse:erlang	28.5.0.4-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
opensuse:erlang27	27.1.3-2.1 · openSUSE:Tumbleweed	Package registry (OSV)
red hat:erlang	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-asn1	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-asn1-debuginfo	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-compiler	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-crypto	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-crypto-debuginfo	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-debuginfo	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-debugsource	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-eldap	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-erl_interface-debuginfo	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-erts	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
red hat:erlang-erts-debuginfo	0:26.2.5.21-2.el9ost · Red Hat:openstack:18.0::el9	Package registry (OSV)
suse:erlang	27.1.3-160000.5.1 · SUSE:Linux Enterprise Server 16.0	Package registry (OSV)
suse:erlang26	26.2.1-150300.7.28.1 · SUSE:Linux Enterprise Module for Server Applications 15 SP7	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

John Downeyfinder
Ingela Anderton Andinremediation developer
Jakub Witczakanalyst
Ada Logicsremediation reviewer

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-427900 days apartnameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification
30Monitor
CVE-2026-3214450 days apartOCSP designated-responder authorization bypass via missing signature verification
30Monitor
CVE-2026-427910 days apartOCSP responder certificate validity period not checked in public_key
25Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: X

Weakness class (CWE)

CWE-295 · Improper Certificate Validation

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:H/SI:H/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

nvd-secondary

Root cause

A certificate validation error is silently swallowed instead of terminating the connection. Often, code added for a test environment makes its way into production.

The bug in code

The whole CWE-295 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

kotlin

1override fun checkServerTrusted(chain: Array<X509Certificate>, type: String) {
2  // Left empty for the test environment
3}

Fixed

kotlin

1val client = OkHttpClient.Builder()
2  .certificatePinner(
3    CertificatePinner.Builder()
4      .add("api.sirius.example", "sha256/…")
5      .build()
6  ).build()

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 8:49 PM UTC
SSVC exploitation— → noneSep 28, 2026, 8:49 PM UTC

For records you follow, these changes also arrive as notifications. →

References

cna.erlef.org/cves/CVE-2026-42789.html

Show all references (11 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records