Vulnerability in php7.4 (DEBIAN-CVE-2021-21708)

Summary

Vulnerability in php7.4 (DEBIAN-CVE-2021-21708). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 7.4.28-1+deb11u1 or later.

Original description

The description as published by the source.

In PHP versions 7.4.x below 7.4.28, 8.0.x below 8.0.16, and 8.1.x below 8.1.3, when using filter functions with FILTER_VALIDATE_FLOAT filter and min/max limits, if the filter fails, there is a possibility to trigger use of allocated memory after free, which can result it crashes, and potentially in overwrite of other memory chunks and RCE. This issue affects: code that uses FILTER_VALIDATE_FLOAT with min/max limits.

Source: OSV.dev (Open Source Vulnerabilities) OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as DEBIAN-CVE-2021-21708 has been found in php7.4.
Successful exploitation can lead to full system takeover.
What to do: upgrade php7.4 to 7.4.28-1+deb11u1 or later.
If unsure, ask your IT team or search "php7.4 DEBIAN-CVE-2021-21708" on the vendor's site.

DEBIAN-CVE-2021-21708 (php7.4)
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 7.4.28-1+deb11u1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (unclassified) exists in php7.4.

📍 Affected scope

Check the vendor advisory for the affected versions of php7.4.

🔥 Severity

Severity: ?. Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 7.4.28-1+deb11u1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'php7.4' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
grep -r 'php7.4' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で php7.4 を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade php7.4 to 7.4.28-1+deb11u1
```
ステージング環境で 7.4.28-1+deb11u1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
3
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Debian:11 php7.4

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"7.4.28-1+deb11u1"}]}]

References

advisory security-tracker.debian.org