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Always-Incorrect Control Flow Implementation in Facebook HermesGHSA-327c-qx3v-h673

CRITICALFix: facebook/hermes@b2021df

GHSA-327c-qx3v-h673 is a critical-severity (CVSS 9.8) CWE-670 vulnerability in hermes-engine. A fix is available for hermes-engine — see the affected versions and patch details below.

Also known asCVE-2020-1914
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs85th percentile — riskier than 85% of all scored CVEsHighest risk
0.35%1.24%2.13%3.02%0.8%2.5%May 26Sep 26Nov 26

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.

hermes-enginenpm
182Kdownloads / week

Description

A logic vulnerability when handling the SaveGeneratorLong instruction in Facebook Hermes prior to commit b2021df620824627f5a8c96615edbd1eb7fdddfc allows attackers to potentially read out of bounds or theoretically execute arbitrary code via crafted JavaScript. Note that this is only exploitable if the application using Hermes permits evaluation of untrusted JavaScript. Hence, most React Native applications are not affected.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
📦npmhermes-engineall versions0.7.2npm install hermes-engine@0.7.2

Affected Products

1 product · 1 configurations
Application
hermesfacebook
< 2020-10-01
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hermes-engine, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update hermes-engine to 0.7.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-327c-qx3v-h673 is resolved across your whole dependency graph.

  3. 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.

Frequently Asked Questions

A logic vulnerability when handling the SaveGeneratorLong instruction in Facebook Hermes prior to commit b2021df620824627f5a8c96615edbd1eb7fdddfc allows attackers to potentially read out of bounds or theoretically execute arbitrary code via crafted JavaScript. Note that this is only exploitable if the application using Hermes permits evaluation of untrusted JavaScript. Hence, most React Native applications are not affected.
O3 Security · Impact-Aware SCA

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