CVE-2018-6335 — A Malformed h2 frame can cause 'std::out_of_range' exception when parsing priority meta data

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HIGH

A Malformed h2 frame can cause 'std::out_of_range' exception when parsing priority meta data

Published Dec 31, 2018

7.5

HIGH

CVSS 3.1

EPSS 1.47%

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.

Affected products

Vendor Facebook Product HHVM Default
n/a
- Version
  3.21.11
  Status
  affected
  Constraints
  -
- Version
  3.22.0
  Status
  affected
  Constraints
  -
- Version
  3.24.7
  Status
  affected
  Constraints
  -
- Version
  3.25.0
  Status
  affected
  Constraints
  -
- Version
  3.25.3
  Status
  affected
  Constraints
  -
- Version
  unspecified
  Status
  affected
  Constraints
  <3.21.11

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor

Product

Default status

Versions

Facebook

HHVM

n/a

Version	Status	Constraints
3.21.11	affected	-
3.22.0	affected	-
3.24.7	affected	-
3.25.0	affected	-
3.25.3	affected	-
unspecified	affected	<3.21.11

Remediation

No remediation recorded yet.

Metrics

1.47% 0.01469

Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 2, 2026.

EPSS probability 0.01469

Score over time

2021–2026

EPSS v1
EPSS v5
EPSS v2
EPSS v3

Percentile over time

EPSS v1
EPSS v5
EPSS v2
EPSS v3

Table of values (9 key points)

Flat stretches are collapsed; showing up to 120 newest points.

Date	Score	Percentile	Model
Oct 2, 2026	1.47% (0.01469)	72.81th	v5 (v2026.06.15)
Sep 20, 2026	1.47% (0.01469)	72.57th	v5 (v2026.06.15)
Jul 20, 2024	0.11% (0.00113)	45.18th	v3 (v2023.03.01)
Jul 3, 2024	0.11% (0.00113)	45.06th	v3 (v2023.03.01)
Mar 7, 2023	0.11% (0.00113)	43.05th	v3 (v2023.03.01)
Mar 6, 2023	0.89% (0.00885)	27.89th	v2 (v2022.01.01)
Feb 4, 2022	0.89% (0.00885)	10.50th	v2 (v2022.01.01)
Feb 3, 2022	0.62% (0.00624)	17.80th	v5 (v2026.06.15)
Apr 14, 2021	0.62% (0.00624)	0.00th	v1

Weaknesses (2)

CWE-20

Improper Input Validation

CWE-400

Uncontrolled Resource Consumption

References (2)

https://github.com/facebook/hhvm/commit/4cb57dd753a339654ca464c139db9871fe961d56
x_refsource_MISCPatchThird Party Advisory
https://hhvm.com/blog/2018/05/04/hhvm-3.25.3.html
x_refsource_MISCVendor Advisory

Link	Providers	Tags
https://github.com/facebook/hhvm/commit/4cb57dd753a339654ca464c139db9871fe961d56		x_refsource_MISCPatchThird Party Advisory
https://hhvm.com/blog/2018/05/04/hhvm-3.25.3.html		x_refsource_MISCVendor Advisory