Downstream response splitting via invalid retry continuation
Published Sep 4, 2026 · Updated Sep 4, 2026
Response splitting in Node.js Undici before 6.28.1, 7.0.0 through 7.29.0, and 8.0.0 through 8.10.1 allows remote attackers to corrupt HTTP responses. The retry interceptor handles status-code retries before validating a continuation, appending bytes from an invalid ranged response after earlier bytes while retaining stale framing headers. Exploitation requires interceptors.retry(), an attacker-controlled upstream, and a forwarder that preserves Content-Length; excess bytes can begin a subsequent downstream response.
Summary
What happened
Response splitting in Node.js Undici before 6.28.1, 7.0.0 through 7.29.0, and 8.0.0 through 8.10.1 allows remote attackers to corrupt HTTP responses. The retry interceptor handles status-code retries before validating a continuation, appending bytes from an invalid ranged response after earlier bytes while retaining stale framing headers. Exploitation requires interceptors.retry(), an attacker-controlled upstream, and a forwarder that preserves Content-Length; excess bytes can begin a subsequent downstream response.
The record
- CVE
- CVE-2026-18540
- Published
- Sep 4, 2026
- Updated
- Sep 4, 2026
- Vendor
- Node.js
- Product
- Undici
- Classifications
- CWE-444
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 4, 2026CVE publishedPublication date reported by the CVE source.
- Sep 4, 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=0 <6.28.1
- Affected versionversion=7.0.0 <7.29.1
- Affected versionversion=8.0.0 <8.10.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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