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CVE-2021-21295 medium CVSS 5.9

Vulnerability in Oracle Apache (CVE-2021-21295)

Summary

Vulnerability in Oracle Apache (CVE-2021-21295). Data can be tampered with by attackers. Exploitable via Http2MultiplexHandler. Mitigation: upgrade to 4.1.60.Final or later.

Original description

The description as published by the source.

Netty is an open-source, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. In Netty (io.netty:netty-codec-http2) before version 4.1.60.Final there is a vulnerability that enables request smuggling. If a Content-Length header is present in the original HTTP/2 request, the field is not validated by Http2MultiplexHandler as it is propagated up. This is fine as long as the request is not proxied through as HTTP/1.1. If the request comes in as an HTTP/2 stream, gets converted into the HTTP/1.1 domain objects (HttpRequest, HttpContent, etc.) via Http2StreamFrameToHttpObjectCodec and then sent up to the child channel's pipeline and proxied through a remote peer as HTTP/1.1 this may result in request smuggling. In a proxy case, users may assume the content-length is validated somehow, which is not the case. If the request is forwarded to a backend channel that is a HTTP/1.1 connection, the Content-Length now has meaning and needs to be checked. An attacker can smuggle requests inside the body as it gets downgraded from HTTP/2 to HTTP/1.1. For an example attack refer to the linked GitHub Advisory. Users are only affected if all of this is true: HTTP2MultiplexCodec or Http2FrameCodec is used, Http2StreamFrameToHttpObjectCodec is used to convert to HTTP/1.1 objects, and these HTTP/1.1 objects are forwarded to another remote peer. This has been patched in 4.1.60.Final As a workaround, t…

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory 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 CVE-2021-21295 has been found in Oracle Apache.
Attackers can target a specific entry point like Http2MultiplexHandler over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 5.9/10.
What to do: upgrade Oracle Apache to 4.1.60.Final or later.
If unsure, ask your IT team or search "Oracle Apache CVE-2021-21295" on the vendor's site.

CVE-2021-21295 (Oracle Apache) — CWE-444 / CVSS v3 5.9
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Http2MultiplexHandler / HttpRequest / HttpContent / HTTP2MultiplexCodec
Patched: 4.1.60.Final — 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 (CWE-444) exists in Oracle Apache. Attackers reach the vulnerable code path via Http2MultiplexHandler without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of Oracle Apache. Attack surface: Http2MultiplexHandler / HttpRequest / HttpContent / HTTP2MultiplexCodec.

🔥 Severity

Severity: Medium (CVSS 5.9/10). Data can be tampered with by attackers.

🔧 How to fix

Update to 4.1.60.Final.

🛡️ 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 'Apache' . 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. 1
    Identify exposure identify 
    grep -r 'Apache' . | 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 Apache を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade Oracle Apache to 4.1.60.Final

    ステージング環境で 4.1.60.Final 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. 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

Maven io.netty:netty-codec-http2
[{"type":"ECOSYSTEM","events":[{"introduced":"4.0.0"},{"fixed":"4.1.60.Final"}]}]
Maven org.jboss.netty:netty
[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}]
Maven io.netty:netty
[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}]
Bitnami zookeeper
[{"type":"SEMVER","events":[{"introduced":"3.5.9"},{"fixed":"3.5.10"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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