Client request hangs via Deflate decoder loop
Published Sep 29, 2026 · Updated Sep 29, 2026
Denial of service in urllib3 2.6.2 through 2.7.0 allows remote attackers controlling an HTTP server to hang streaming client requests. In HTTPResponse.stream and read_chunked, the Deflate decoder repeatedly retries trailing encoded bytes after the compressed stream ends without making progress or reading the socket. Exposure requires enabled decoding of a chunked Deflate response with trailing bytes and a decoded body larger than the positive finite streaming chunk size; the loop consumes CPU and evades network read timeouts.
Summary
What happened
Denial of service in urllib3 2.6.2 through 2.7.0 allows remote attackers controlling an HTTP server to hang streaming client requests. In HTTPResponse.stream and read_chunked, the Deflate decoder repeatedly retries trailing encoded bytes after the compressed stream ends without making progress or reading the socket. Exposure requires enabled decoding of a chunked Deflate response with trailing bytes and a decoded body larger than the positive finite streaming chunk size; the loop consumes CPU and evades network read timeouts.
The record
- CVE
- CVE-2026-97688
- Published
- Sep 29, 2026
- Updated
- Sep 29, 2026
- Vendor
- urllib3
- Product
- urllib3
- Classifications
- CWE-835, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 29, 2026CVE publishedPublication date reported by the CVE source.
- Sep 29, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 2.6.2, < 2.8.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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