Summary
hex_core has Unsafe Deserialization of Erlang Terms
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.
Resources
- 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: https://github.com/hexpm/hex_core/commit/cdf726095bca85ad2549d146df1e831ae93c2b13
- Hex Vendored Patch: https://github.com/hexpm/hex/commit/636739f3322514e9303ca335fb630696fcbb3c95
- Rebar3 Vendored Patch: https://github.com/erlang/rebar3/commit/1d4478f527e373de0b225951e53115450e0d9b9d
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.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-21619? CVE-2026-21619 is a low-severity uncontrolled resource consumption vulnerability in hex_core (erlang), affecting versions < 0.12.1. It is fixed in 0.12.1. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- Which versions of hex_core are affected by CVE-2026-21619? hex_core (erlang) versions < 0.12.1 is affected.
- Is there a fix for CVE-2026-21619? Yes. CVE-2026-21619 is fixed in 0.12.1. Upgrade to this version or later.
- Is CVE-2026-21619 exploitable, and should I be worried? Whether CVE-2026-21619 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-21619 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-21619? Upgrade
hex_coreto 0.12.1 or later.