How severe is CVE-2026-21619?

No CVSS score has been assigned to CVE-2026-21619 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-21619?

CVE-2026-21619 affects the following packages: hex_core (Hex). Ecosystems affected: Hex.

How do I fix CVE-2026-21619?

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.

How do I detect CVE-2026-21619 in my Hex dependencies?

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.

How do I mitigate CVE-2026-21619 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2026-21619 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-21619 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-21619?

CVE-2026-21619 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 51th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-21619?

CVE-2026-21619 is classified as Uncontrolled Resource Consumption (CWE-400), Deserialization of Untrusted Data (CWE-502). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-21619 published, and has it been updated?

CVE-2026-21619 was published on February 27, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💧 Hex

Not in CISA KEV

CVE-2026-21619 — hex_core

Fix: erlang/rebar3@1d4478f

CVE-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

Also known asEEF-CVE-2026-21619GHSA-hx9w-f2w9-9g96

Published

Feb 27, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs51th percentile — riskier than 51% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

💧hex_core

Real-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

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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💧Hex	`hex_core`	all versions	0.12.1`mix deps.update hex_core`

Affected Products

3 products · 3 configurations

Application

rebar3erlang

≥ 3.9.1 && < 3.27.0

range

Application

hexhex

≥ 2.3.0 && < 2.3.2

range

Application

hex corehex

≥ 0.1.0 && < 0.12.1

range

Detection & mitigation playbook

Open-source dependency

Detect
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
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Frequently Asked Questions

### 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/com

O3 Security · Impact-Aware SCA

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