CVE-2026-21619 — hex_core
Fix: erlang/rebar3@1d4478fCVE-2026-21619 is a Uncontrolled Resource Consumption vulnerability in hex_core. A fix is available for hex_core — see the affected versions and patch details below.
Unsafe Deserialization of Erlang Terms in hex_core
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-21619.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
hex_coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Hex packages — download data is not available via public APIs for these ecosystems.
Description
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.
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💧Hex | hex_core | all versions | 0.12.1mix deps.update hex_core |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hex_core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hex_core to 0.12.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-21619 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-21619 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-21619. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-21619 in your dependencies?
O3 Security finds CVE-2026-21619 across Hex dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.