How severe is CVE-2021-24025?

CVE-2021-24025 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-2021-24025 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-24025?

CVE-2021-24025 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-2021-24025?

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-2021-24025 published?

CVE-2021-24025 was published on 2021-03-10 and last updated on 2026-06-17.

CVE-2021-24025

CVE-2021-24025 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-190.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (74th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-190
Affected product: Facebook Hhvm
Published: 2021-03-10
Last modified: 2026-06-17

Description

Due to incorrect string size calculations inside the preg_quote function, a large input string passed to the function can trigger an integer overflow leading to a heap overflow. This issue affects HHVM versions prior to 4.56.3, all versions between 4.57.0 and 4.80.1, all versions between 4.81.0 and 4.93.1, and versions 4.94.0, 4.95.0, 4.96.0, 4.97.0, 4.98.0.

Frequently asked questions

What is CVE-2021-24025?: Due to incorrect string size calculations inside the preg_quote function, a large input string passed to the function can trigger an integer overflow leading to a heap overflow. This issue affects HHVM versions prior to 4.56.3, all versions between 4.57.0 and 4.80.1, all versions between 4.81.0 and 4.93.1, and versions 4.94.0, 4.95.0, 4.96.0, 4.97.0, 4.98.0.
How severe is CVE-2021-24025?: CVE-2021-24025 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-2021-24025 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (74th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-24025?: CVE-2021-24025 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-2021-24025?: 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-2021-24025 published?: CVE-2021-24025 was published on 2021-03-10 and last updated on 2026-06-17.

References

Affected products (6)

cpe:2.3:a:facebook:hhvm:*:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.94.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.95.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.96.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.97.0:*:*:*:*:*:*:*
cpe:2.3:a:facebook:hhvm:4.98.0:*:*:*:*:*:*:*

More vulnerabilities in Facebook Hhvm

CVE-2022-36937 — Critical (CVSS 9.8): HHVM 4.172.0 and all prior versions use TLS 1.0 for secure connections when handling tls:// URLs in the stream…
CVE-2021-24036 — Critical (CVSS 9.8): Passing an attacker controlled size when creating an IOBuf could cause integer overflow, leading to an out of bounds…
CVE-2020-1900 — Critical (CVSS 9.8): When unserializing an object with dynamic properties HHVM needs to pre-reserve the full size of the dynamic property…
CVE-2020-1917 — Critical (CVSS 9.8): xbuf_format_converter, used as part of exif_read_data, was appending a terminating null character to the generated…
CVE-2020-1916 — Critical (CVSS 9.8): An incorrect size calculation in ldap_escape may lead to an integer overflow when overly long input is passed in,…
CVE-2016-1000005 — Critical (CVSS 9.8): mcrypt_get_block_size did not enforce that the provided "module" parameter was a string, leading to type confusion if…

All CVEs affecting Facebook Hhvm →

Other CWE-190 (Integer Overflow or Wraparound) vulnerabilities

CVE-2026-4689 — Critical (CVSS 10.0): Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component. This vulnerability was…
CVE-2026-24814 — Critical (CVSS 10.0): Integer Overflow or Wraparound vulnerability in swoole swoole-src (thirdparty/hiredis modules). This vulnerability is…
CVE-2025-64721 — Critical (CVSS 10.0): Sandboxie is a sandbox-based isolation software for 32-bit and 64-bit Windows NT-based operating systems. In versions…
CVE-2015-5108 — Critical (CVSS 10.0): Integer overflow in Adobe Reader and Acrobat 10.x before 10.1.15 and 11.x before 11.0.12, Acrobat and Acrobat Reader DC…
CVE-2015-5097 — Critical (CVSS 10.0): Integer overflow in Adobe Reader and Acrobat 10.x before 10.1.15 and 11.x before 11.0.12, Acrobat and Acrobat Reader DC…
CVE-2013-2555 — Critical (CVSS 10.0): Integer overflow in Adobe Flash Player before 10.3.183.75 and 11.x before 11.7.700.169 on Windows and Mac OS X, before…

Browse all CWE-190 (Integer Overflow or Wraparound) vulnerabilities →