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Message-ID: <6579b4c2-c2d2-4059-8d89-fada89a9534d@oracle.com>
Date: Sun, 12 Apr 2026 13:15:17 -0700
From: Alan Coopersmith <alan.coopersmith@...cle.com>
To: oss-security@...ts.openwall.com
Subject: Security Audit of Hex, the Erlang package manager
https://hex.pm/blog/security-audit announces the completion of a
security audit & penetration testing of Hex, the Erlang package manager,
funded by the OpenSSF and overseen by the Erlang Ecosystem Foundation.
This work was done by two independent security firms, Paraxial.io and
zentrust partners GmbH, who each produced their own reports:
- https://hex.pm/reports/2026/paraxial.pdf
- https://hex.pm/reports/2026/zentrust.pdf
The announcement reports:
> What was found
> --------------
>
> Across both audits, a number of issues were identified, ranging from high
> severity vulnerabilities to low-severity hardening gaps.
>
> Examples include:
>
> * Unsafe deserialization in hex_core that could lead to RCE under certain
> conditions
> * A denial of service condition during package uploads
> * Weaknesses in authentication flows and API key handling
> * Gaps in CI/CD hardening (GitHub Actions)
> * Missing or incomplete security controls in some areas
>
> Importantly, the audits focused on realistic attack scenarios such as:
>
> * cross-account package tampering
> * bypassing integrity checks
> * injection in public-facing features
> * CI/CD compromise
>
> What we fixed
> -------------
>
> Most findings have been remediated during the engagement and confirmed in
> re-tests.
>
> Highlights:
>
> * Fixed unsafe deserialization in hex_core (CVE-2026-21619)
> * Fixed API key privilege escalation (CVE-2026-21621)
> * Fixed password reset issues (CVE-2026-21622)
> * Fixed XSS in OAuth device flow (CVE-2026-21618)
> * Fixed denial of service in package upload (CVE-2026-23940)
> * Removed sensitive credentials from repositories
> * Hardened authentication flows (including "sudo mode" for sensitive actions)
> * Disabled legacy TLS versions
> * Improved CSP and other browser security controls
>
> Re-tests by both firms confirmed that the majority of vulnerabilities were
> successfully remediated.
>
> Several remaining items are either:
>
> * accepted risks with clear rationale (for example UX trade-offs or staged
> migrations), or
> * dependent on ecosystem-wide changes (for example client updates)
>
> What we decided not to change (yet)
> -----------------------------------
>
> Some findings reflect intentional trade-offs or transitional states rather
> than vulnerabilities.
>
> Examples:
>
> * Basic authentication and optional 2FA are still supported for compatibility
> with existing clients. Both will be phased out once all clients support the
> OAuth2 device flow.
> * Certain features (like documentation hosting) intentionally allow
> user-provided content and are being isolated rather than restricted.
>
> These decisions were reviewed jointly by the Hex.pm team and the EEF.
These issues appear to be reported against the hexpm server side, not the client
side that end users & distros are likely to be running:
- Cross-site scripting (XSS) in OAuth Device Authorization screen (CVE-2026-21618)
https://github.com/hexpm/hexpm/security/advisories/GHSA-6cw9-5gg4-rhpj
- Improper Scope Enforcement in OAuth client_credentials Flow Allows Read-Only
API Key to Escalate to Full Access with Valid 2FA Code (CVE-2026-21621)
https://github.com/hexpm/hexpm/security/advisories/GHSA-739m-8727-j6w3
- Password Reset Tokens Do Not Expire (CVE-2026-21622)
https://github.com/hexpm/hexpm/security/advisories/GHSA-6r94-pvwf-mxqm
- Path Traversal in Local File Store Backend (Development and Self-Hosted
Registry Setups) (CVE-2026-23939)
https://github.com/hexpm/hexpm/security/advisories/GHSA-42mv-r64p-4869
- Publishing Oversized Package Can Trigger Denial of Service (CVE-2026-23940)
https://github.com/hexpm/hexpm/security/advisories/GHSA-jp8w-gxf6-8hcr
That leaves one CVE for distros and end users to worry about -
https://github.com/hexpm/hex_core/security/advisories/GHSA-hx9w-f2w9-9g96 reports:
> Unsafe Deserialization of Erlang Terms in hex_core
> --------------------------------------------------
>
> maennchen published GHSA-hx9w-f2w9-9g96 Feb 27, 2026
>
> Package: hex (otp)
> Affected versions: >= 2.3.0 and <= 2.3.2
> Patched versions: 2.3.2
>
> Package: hex_core (Erlang)
> Affected versions: <= 0.12.1
> Patched versions: 0.12.1
>
> Package: rebar3 (otp)
> Affected versions: >= 3.9.1 and <= 3.27.0
> Patched versions: 3.27.0
>
> Impact
> ------
> The Hex client (hex_core) deserializes Erlang terms received from the
> Hex API using binary_to_term/1 without sufficient restrictions.
>
> If an attacker can control the HTTP response body returned by the Hex API,
> this allows denial-of-service attacks such as atom table exhaustion, leading
> to a VM crash. No released versions are known to allow remote code execution.
>
> Patches
> -------
> https://github.com/hexpm/hex_core/commit/cdf726095bca85ad2549d146df1e831ae93c2b13
> https://github.com/hexpm/hex/commit/636739f3322514e9303ca335fb630696fcbb3c95
> https://github.com/erlang/rebar3/commit/1d4478f527e373de0b225951e53115450e0d9b9d
>
> Workarounds
> -----------
> Ensure that the Hex API URL (HEX_API_URL) points only to trusted endpoints.
> There is no client-side workaround that fully mitigates this issue without
> applying the patch.
>
> References
> ----------
> - hex_core Module: https://github.com/hexpm/hex_core/blob/main/src/hex_api.erl
> - Hex Vendored Module: https://github.com/hexpm/hex/blob/main/src/mix_hex_api.erl
> - Rebar3 Vendored Module: https://github.com/erlang/rebar3/blob/main/apps/rebar/src/vendored/r3_hex_api.erl
> - hex_core Patch: cdf7260
> - Hex Vendored Patch: hexpm/hex@...739f
> - Rebar3 Vendored Patch: erlang/rebar3@...478f
>
> Severity: Low - 2.0 / 10
> CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
> CVE ID: CVE-2026-21619
> Weaknesses:
> - CWE-400: Uncontrolled Resource Consumption
> - CWE-502: Deserialization of Untrusted Data
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