Security Bulletin
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 29.0.1, OTP 28.5.0.1, OTP 27.3.4.12 and OTP 26.2.5.21, corresponding to public_key from 1.4 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.
Vulnerability Details
CVEID: CVE-2026-42790
DESCRIPTION: 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 29.0.1, OTP 28.5.0.1, OTP 27.3.4.12 and OTP 26.2.5.21, corresponding to public_key from 1.4 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.
CWE: CWE-295: Improper Certificate Validation
CVSS Source: NVD
CVSS Base score: 8.1
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N)
CVEID: CVE-2026-48856
DESCRIPTION: Sensitive Data Exposure vulnerability in Erlang OTP inets (httpc_response module) allows Retrieve Embedded Sensitive Data.
The httpc client forwards the Authorization and Proxy-Authorization request headers to redirect targets without checking whether the redirect crosses an origin boundary. httpc_response:redirect/2 constructs the redirected request by updating only the host field of the header record; all other fields (including authorization and proxy_authorization) are copied verbatim. The redirect target host is never compared against the original host.
autoredirect defaults to true, so this affects all httpc callers that do not explicitly disable automatic redirects.
An attacker who controls a server that the victim contacts via httpc can issue a cross-origin 3xx redirect to a server they also control. The Authorization header (including Basic credentials derived from URL userinfo via httpc_request:handle_user_info/2) is forwarded to the redirect target, allowing credential theft. The same applies to the Proxy-Authorization header.
This vulnerability is associated with program files lib/inets/src/http_client/httpc_response.erl.
This issue affects OTP from OTP 17.0 before OTP 27.3.4.13, OTP 28.5.0.2, and OTP 29.0.2, corresponding to inets from 5.10 before 9.3.2.6, 9.6.2.2, and 9.7.1. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
CWE: CWE-601: URL Redirection to Untrusted Site ('Open Redirect')
CVSS Source: NVD
CVSS Base score: 6.5
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N)
CVEID: CVE-2026-49760
DESCRIPTION: Stack-based Buffer Overflow vulnerability in Erlang OTP (erl_interface) allows Stack-based Buffer Overflow.
This vulnerability is associated with program file lib/erl_interface/src/misc/ei_printterm.c and program routine ei_s_print_term.
The C function ei_s_print_term uses an internal 2000-character stack buffer to format terms. When called with an encoded Erlang term containing a very large integer (encoded representation exceeding 2000 characters), the buffer overflows. The overflow bytes are restricted to the ASCII values of 0-9 and A-F, which limits exploitation to Denial of Service.
The companion function ei_print_term, which prints directly to a FILE instead of a memory buffer, does not contain this bug.
This issue affects OTP from OTP 17.0 before OTP 27.3.4.13, OTP 28.5.0.2, and OTP 29.0.2, corresponding to erl_interface from 3.7.16 before 5.5.2.1, 5.7.0.1, and 5.8.1. Whether OTP before OTP 17.0, corresponding to erl_interface before 3.7.16, is affected is unknown.
CWE: CWE-121: Stack-based Buffer Overflow
CVSS Source: NVD
CVSS Base score: 5.5
CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| PowerVC | 2.3.1, 2.3.2, 2.3.3 |
Remediation/Fixes
PowerVC Version | Remediation
--------------------------------------------------------------------------------
2.3.1 | Please update to PowerVC 2.3.2 or 2.3.3
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
Workarounds and Mitigations
None
Get Notified about Future Security Bulletins
References
Acknowledgement
Change History
06 Oct 2026: Initial Publication
*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.
Disclaimer
According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.
Document Location
Worldwide
Was this topic helpful?
Document Information
Modified date:
06 October 2026
Initial Publish date:
06 October 2026
UID
ibm17291406