Security readout for executives and security teams
Plain-English summary
HHVM could mishandle multipart file uploads by placing variables into global scope unexpectedly. In vulnerable applications, especially where variables are used without explicit declaration, an unauthenticated network request may cause severe confidentiality, integrity, and availability impact.
Executive priority
Treat as urgent for any business-critical HHVM service exposed to uploads. The maximum CVSS score and unauthenticated network vector justify rapid inventory and patch planning, even without evidence of active exploitation.
Technical view
CVE-2018-6334 is a HHVM multipart upload variable-registration flaw mapped to CWE-621. The supplied CVSS 3.1 vector is network, low complexity, no privileges, no user interaction, with high impact across confidentiality, integrity, and availability.
Likely exposure
Exposure is limited to systems running affected Facebook HHVM versions that accept multipart file uploads. The bundle states all supported HHVM versions before the patch are affected, but its version list appears inconsistent, so verify against vendor guidance.
Exploitation context
The source bundle does not cite active exploitation, and KEV is false. The CVSS vector indicates potential remote unauthenticated exploitation, but no public exploit status is established by the provided sources.
Researcher notes
The key uncertainty is version scoping: the narrative says versions prior to the patch are affected, while the bundled affected list includes versions that may need vendor confirmation. Avoid assuming exploitability in applications that do not process multipart uploads.
Mitigation direction
- Inventory production and internet-facing HHVM services.
- Prioritize systems handling multipart file uploads.
- Upgrade HHVM according to the cited vendor release guidance.
- Review code for undeclared variables in upload-handling paths.
- Monitor vendor advisories for version-specific correction details.
Validation and detection
- Confirm HHVM versions deployed across hosts and containers.
- Identify routes accepting multipart file uploads.
- Check vendor release notes for the fixed HHVM branch version.
- Review application logs for anomalous upload behavior.
- Confirm patched systems no longer run affected HHVM builds.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-621: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2018-6334 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/facebook/hhvm/commit/6937de5544c3eead3466b75020d8382080ed0cffCVE reference · x_refsource_MISC
- https://hhvm.com/blog/2018/03/30/hhvm-3.25.2.htmlCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Variable Extraction Error
Variable Extraction Error represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.