How severe is CVE-2020-1900?

CVE-2020-1900 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2020-1900 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-1900?

CVE-2020-1900 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-2020-1900?

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

When was CVE-2020-1900 published?

CVE-2020-1900 was published on 2021-03-11 and last updated on 2026-06-17.

CVE-2020-1900

CVE-2020-1900 is a critical-severity vulnerability in Facebook Hhvm with a CVSS 3.x base score of 9.8. 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-416.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 1% (69th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-416
Affected product: Facebook Hhvm
Published: 2021-03-11
Last modified: 2026-06-17

Description

When unserializing an object with dynamic properties HHVM needs to pre-reserve the full size of the dynamic property array before inserting anything into it. Otherwise the array might resize, invalidating previously stored references. This pre-reservation was not occurring in 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-2020-1900?: When unserializing an object with dynamic properties HHVM needs to pre-reserve the full size of the dynamic property array before inserting anything into it. Otherwise the array might resize, invalidating previously stored references. This pre-reservation was not occurring in 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-2020-1900?: CVE-2020-1900 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2020-1900 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-1900?: CVE-2020-1900 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-2020-1900?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2020-1900 published?: CVE-2020-1900 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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CVE-2025-24085 — Critical (CVSS 10.0): A use after free issue was addressed with improved memory management. This issue is fixed in iOS 18.3 and iPadOS 18.3,…
CVE-2024-43102 — Critical (CVSS 10.0): Concurrent removals of certain anonymous shared memory mappings by using the UMTX_SHM_DESTROY sub-request of…
CVE-2021-32495 — Critical (CVSS 10.0): Radare2 has a use-after-free vulnerability in pyc parser's get_none_object function. Attacker can read freed memory…

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