CVE-2019-3556
CVE-2019-3556 is a high-severity vulnerability in Facebook Hhvm with a CVSS 3.x base score of 8.1. 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-22.
Key facts
- Severity: High (CVSS 3.x base score 8.1)
- CVSS v2: 5.5
- EPSS exploit prediction: 2% (75th percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-22
- Affected product: Facebook Hhvm
- Published:
- Last modified:
Description
HHVM supports the use of an "admin" server which accepts administrative requests over HTTP. One of those request handlers, dump-pcre-cache, can be used to output cached regular expressions from the current execution context into a file. The handler takes a parameter which specifies where on the filesystem to write this data. The parameter is not validated, allowing a malicious user to overwrite arbitrary files where the user running HHVM has write access. This issue affects HHVM versions prior to 4.56.2, all versions between 4.57.0 and 4.78.0, as well as 4.79.0, 4.80.0, 4.81.0, 4.82.0, and 4.83.0.
Frequently asked questions
- What is CVE-2019-3556?
- HHVM supports the use of an "admin" server which accepts administrative requests over HTTP. One of those request handlers, dump-pcre-cache, can be used to output cached regular expressions from the current execution context into a file. The handler takes a parameter which specifies where on the filesystem to write this data. The parameter is not validated, allowing a malicious user to overwrite arbitrary files where the user running HHVM has write access. This issue affects HHVM versions prior to 4.56.2, all versions between 4.57.0 and 4.78.0, as well as 4.79.0, 4.80.0, 4.81.0, 4.82.0, and 4.83.0.
- How severe is CVE-2019-3556?
- CVE-2019-3556 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.
- Is CVE-2019-3556 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2019-3556?
- CVE-2019-3556 primarily affects Facebook Hhvm. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
- How do I fix CVE-2019-3556?
- 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-2019-3556 published?
- CVE-2019-3556 was published on 2021-10-26 and last updated on 2026-06-17.
References
- https://github.com/facebook/hhvm/commit/abe0b29e4d3a610f9bc920b8be4ad8403364c2d4
- https://hhvm.com/blog/2020/11/12/security-update.html
- https://www.facebook.com/security/advisories/cve-2019-3556
Affected products (6)
- cpe:2.3:a:facebook:hhvm:*:*:*:*:*:*:*:*
- cpe:2.3:a:facebook:hhvm:4.79.0:*:*:*:*:*:*:*
- cpe:2.3:a:facebook:hhvm:4.80.0:*:*:*:*:*:*:*
- cpe:2.3:a:facebook:hhvm:4.81.0:*:*:*:*:*:*:*
- cpe:2.3:a:facebook:hhvm:4.82.0:*:*:*:*:*:*:*
- cpe:2.3:a:facebook:hhvm:4.83.0:*:*:*:*:*:*:*
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