How severe is CVE-2018-6335?

CVE-2018-6335 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2018-6335 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-6335?

CVE-2018-6335 primarily affects Facebook Hhvm. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2018-6335?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2018-6335 published?

CVE-2018-6335 was published on 2018-12-31 and last updated on 2026-06-17.

CVE-2018-6335

CVE-2018-6335 is a high-severity vulnerability in Facebook Hhvm with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (71st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Facebook Hhvm
Published: 2018-12-31
Last modified: 2026-06-17

Description

A Malformed h2 frame can cause 'std::out_of_range' exception when parsing priority meta data. This behavior can lead to denial-of-service. This affects all supported versions of HHVM (3.25.2, 3.24.6, and 3.21.10 and below) when using the proxygen server to handle HTTP2 requests.

Frequently asked questions

What is CVE-2018-6335?: A Malformed h2 frame can cause 'std::out_of_range' exception when parsing priority meta data. This behavior can lead to denial-of-service. This affects all supported versions of HHVM (3.25.2, 3.24.6, and 3.21.10 and below) when using the proxygen server to handle HTTP2 requests.
How severe is CVE-2018-6335?: CVE-2018-6335 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2018-6335 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2018-6335?: CVE-2018-6335 primarily affects Facebook Hhvm. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2018-6335?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2018-6335 published?: CVE-2018-6335 was published on 2018-12-31 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:facebook:hhvm:*:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:3.24.6:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:3.25.2:*:*:*:*:*:*:*

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