How severe is CVE-2021-37704?

CVE-2021-37704 has a CVSS score of 4.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-37704?

CVE-2021-37704 affects the following packages: phpfastcache/phpfastcache (Packagist), phpfastcache/phpfastcache (Packagist), phpfastcache/phpfastcache (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-37704?

Update phpfastcache/phpfastcache to 6.1.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-37704 is resolved across your whole dependency graph.

How do I detect CVE-2021-37704 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phpfastcache/phpfastcache, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-37704 if there is no patch (or I can't update yet)?

Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Is CVE-2021-37704 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-37704, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-37704?

CVE-2021-37704 has an EPSS (Exploit Prediction Scoring System) score of 6.1%, placing it in the 93th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-37704?

CVE-2021-37704 is classified as Information Exposure (CWE-200), CWE-668 (CWE-668). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2021-37704?

A Nuclei detection template exists for CVE-2021-37704, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-37704 published, and has it been updated?

CVE-2021-37704 was published on August 12, 2021 and was last updated on August 27, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

MEDIUM severity

CVE-2021-37704 — phpfastcache

MEDIUMFix: PHPSocialNetwork/phpfastcache@41a77d0

CVE-2021-37704 is a medium-severity (CVSS 4.3) Information Exposure vulnerability in phpfastcache/phpfastcache. 1 public exploit reference exists, so weaponization risk is real. A fix is available for phpfastcache/phpfastcache — see the affected versions and patch details below.

Exposed phpinfo() leadked via documentation files

Also known asGHSA-cvh5-p6r6-g2qc

Published

Aug 12, 2021

Updated

Aug 27, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

1 known

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

6.1%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs93th percentile — riskier than 93% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-37704 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

3 pkgs affected

🐘phpfastcache/phpfastcache🐘phpfastcache/phpfastcache🐘phpfastcache/phpfastcache

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

Impact

The phpinfo() can be exposed if the /vendor is not protected from public access. This is a rare situation today since the vendor directory is often located outside the web directory or protected via server rule (.htaccess, etc).

Patches

Only the v6, v7 and v8 will be patched respectively in 8.0.7, 7.1.2, 6.1.5. Older versions such as v5, v4 are not longer supported and will NOT be patched.

Workarounds

Protect the /vendor directory from public access.

References

The first issue revealing this vulnerability is located here: https://github.com/flextype/flextype/issues/567 V6 fix: https://github.com/PHPSocialNetwork/phpfastcache/pull/815 V7 fix: https://github.com/PHPSocialNetwork/phpfastcache/pull/814 V8 fix: https://github.com/PHPSocialNetwork/phpfastcache/pull/813

For more information

If you have any questions or comments about this advisory:

Open an issue in our issue tracker
Email us at [email protected]

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`phpfastcache/phpfastcache`	all versions	6.1.5`composer require phpfastcache/phpfastcache:^6.1.5`
🐘Packagist	`phpfastcache/phpfastcache`	≥ 7.0.0&&< 7.1.2	7.1.2`composer require phpfastcache/phpfastcache:^7.1.2`
🐘Packagist	`phpfastcache/phpfastcache`	≥ 8.0.0&&< 8.0.7	8.0.7`composer require phpfastcache/phpfastcache:^8.0.7`

Affected Products

1 product · 3 configurations

Application

phpfastcachephpfastcache

≥ 8.0.0 && < 8.0.7

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

PhpFastCache is a high-performance backend cache system (packagist packa…

github.comNVDAug 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phpfastcache/phpfastcache, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update phpfastcache/phpfastcache to 6.1.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-37704 is resolved across your whole dependency graph.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

How to detect CVE-2021-37704

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2021-37704 -u https://target

Template: phpfastcache - phpinfo Resource Exposure
Severity: medium
Impact: An attacker can gain access to sensitive information, such as server configuration details, PHP version, and installed extensions.
Remediation: Remove or restrict access to the phpinfo.php file in the phpfastcache library.

Template by ProjectDiscovery nuclei-templates (whoever), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

### Impact The `phpinfo()` can be exposed if the `/vendor` is not protected from public access. This is a rare situation today since the vendor directory is often located outside the web directory or protected via server rule (.htaccess, etc). ### Patches Only the v6, v7 and v8 will be patched respectively in 8.0.7, 7.1.2, 6.1.5. Older versions such as v5, v4 are not longer supported and will **NOT** be patched. ### Workarounds Protect the `/vendor` directory from public access. ### References The first issue revealing this vulnerability is located here: https://github.com/flextype/flextype