How severe is CVE-2020-1899?

CVE-2020-1899 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 high, integrity none, and availability none.

Is CVE-2020-1899 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-1899?

CVE-2020-1899 primarily affects Facebook Hhvm. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-1899?

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-2020-1899 published?

CVE-2020-1899 was published on 2021-03-11 and last updated on 2026-06-17.

CVE-2020-1899

CVE-2020-1899 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-119.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (65th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-119
Affected product: Facebook Hhvm
Published: 2021-03-11
Last modified: 2026-06-17

Description

The unserialize() function supported a type code, "S", which was meant to be supported only for APC serialization. This type code allowed arbitrary memory addresses to be accessed as if they were static StringData objects. This issue affected HHVM prior to v4.32.3, between versions 4.33.0 and 4.56.0, 4.57.0, 4.58.0, 4.58.1, 4.59.0, 4.60.0, 4.61.0, 4.62.0.

Frequently asked questions

What is CVE-2020-1899?: The unserialize() function supported a type code, "S", which was meant to be supported only for APC serialization. This type code allowed arbitrary memory addresses to be accessed as if they were static StringData objects. This issue affected HHVM prior to v4.32.3, between versions 4.33.0 and 4.56.0, 4.57.0, 4.58.0, 4.58.1, 4.59.0, 4.60.0, 4.61.0, 4.62.0.
How severe is CVE-2020-1899?: CVE-2020-1899 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 high, integrity none, and availability none.
Is CVE-2020-1899 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (65th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-1899?: CVE-2020-1899 primarily affects Facebook Hhvm. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-1899?: 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-2020-1899 published?: CVE-2020-1899 was published on 2021-03-11 and last updated on 2026-06-17.

References

Affected products (8)

cpe:2.3:a:facebook:hhvm:*:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.57.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.58.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.58.1:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.59.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.60.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.61.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.62.0:*:*:*:*:*:*:*

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