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CVE-2026-97688 medium CVSS 5.3

Vulnerability in urllib3 (CVE-2026-97688)

Summary

Vulnerability in urllib3 (CVE-2026-97688). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 2.8.0 or later.

Original description

The description as published by the source.

Impact

urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading content in chunks instead of loading the entire response body into memory at once.

urllib3 can decompress response bodies according to the HTTP Content-Encoding header. When streaming a compressed, chunked response, urllib3 first consumes data already buffered by the decoder before reading the next HTTP chunk.

However, urllib3 versions from 2.6.2 through 2.7.0 could enter an infinite loop when a chunked response contained bytes after the end of the Deflate stream. If the decompressed body exceeded the requested streaming chunk size, Python's zlib implementation could retain the trailing bytes as unconsumed input after reaching the end of the compressed stream. urllib3 would repeatedly attempt to decode those same bytes without making progress or reading more data from the network.

A malicious server could exploit this behavior to cause excessive CPU usage and prevent the affected request from completing on the client. Network read timeouts would not interrupt the loop because no further socket operation was required.

Affected usages

Applications and libraries using urllib3 versions 2.6.2 through 2.7.0 may be affected when all of the following conditions are met:

  1. Compressed responses from an untrusted source are streamed using HTTPResponse.stream(amt=N) or HTTPResponse.read_chunked(amt=N) with a positive, finite chunk size.
  2. Content decoding is ena…

Source: NIST National Vulnerability Database NVD GitHub Advisory

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-2026-97688 has been found in urllib3.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade urllib3 to 2.8.0 or later.
If unsure, ask your IT team or search "urllib3 CVE-2026-97688" on the vendor's site.

CVE-2026-97688 (urllib3) — CWE-835 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 2.8.0 — apply immediately
Workaround: disable automatic content decoding for responses from untrusted sources by setting decode_content=False, or reject streamed responses using the Deflate content encoding.
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-835) exists in urllib3.

📍 Affected scope

Check the vendor advisory for the affected versions of urllib3.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.8.0.

🛡️ Workaround

Workaround: disable automatic content decoding for responses from untrusted sources by setting decode_content=False, or reject streamed responses using the Deflate content encoding.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'urllib3' . 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 'urllib3' . | 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 urllib3 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 temporary workaround mitigate 
    disable automatic content decoding for responses from untrusted sources by setting `decode_content=False`, or reject streamed responses using the Deflate content encoding.

    パッチが適用されるまでの応急処置として、disable automatic content decoding for responses from untrusted sources by setting decode_content=False, or reject streamed responses using the Deflate content encoding. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply patch patch 
    Upgrade urllib3 to 2.8.0

    ステージング環境で 2.8.0 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。

  4. 4
    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

pip urllib3
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.8.0"}]}]

References

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