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CRITICAL severity

Use After Free in HermesGHSA-mph8-6787-r8hw

CRITICALFix: facebook/hermes@d86e185

GHSA-mph8-6787-r8hw is a critical-severity (CVSS 9.8) Use After Free vulnerability in hermes-engine. A fix is available for hermes-engine — see the affected versions and patch details below.

Also known asCVE-2021-24037
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs78th percentile — riskier than 78% of all scored CVEsHighest risk
0.03%0.79%1.54%2.29%0.5%1.8%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
199Kdownloads / week

Description

A use after free in hermes, while emitting certain error messages, prior to commit d86e185e485b6330216dee8e854455c694e3a36e allows attackers to potentially 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 versions0.8.0npm install hermes-engine@0.8.0

Affected Products

1 product · 1 configurations
Application
hermesfacebook
< 0.8.0
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 0.8.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mph8-6787-r8hw is resolved across your whole dependency graph.

  3. Workarounds

    Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Frequently Asked Questions

A use after free in hermes, while emitting certain error messages, prior to commit d86e185e485b6330216dee8e854455c694e3a36e allows attackers to potentially 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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Use After Free in Hermes (Critical 9.8)