Response poisoning via sign-tolerant chunk-size parsing
Published Jul 16, 2026 · Updated Jul 16, 2026
HTTP response smuggling in Elixir Mint's Mint 0.1.0 through 1.9.2 allows remote attackers to poison queued responses via signed chunk sizes. Mint.HTTP1.decode_body/5 passes each HTTP/1 chunk-size line to Integer.parse/2, which accepts forbidden leading plus and minus signs and treats signed zero as the body terminator. Exploitation requires a strict intermediary and reused HTTP/1 connection; injected bytes can replace the headers, status, or body returned for another request.
Summary
What happened
HTTP response smuggling in Elixir Mint's Mint 0.1.0 through 1.9.2 allows remote attackers to poison queued responses via signed chunk sizes. Mint.HTTP1.decode_body/5 passes each HTTP/1 chunk-size line to Integer.parse/2, which accepts forbidden leading plus and minus signs and treats signed zero as the body terminator. Exploitation requires a strict intermediary and reused HTTP/1 connection; injected bytes can replace the headers, status, or body returned for another request.
The record
- CVE
- CVE-2026-59249
- Published
- Jul 16, 2026
- Updated
- Jul 16, 2026
- Vendor
- Elixir Mint
- Product
- Mint
- Classifications
- CWE-444, CAPEC-273
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 16, 2026CVE publishedPublication date reported by the CVE source.
- Jul 16, 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=0.1.0 <1.9.3
- Affected versionversion=60089586ec7adc9fddb09f69a2f5919ba9ac7f33 <fc7d16538db7e40b56ed489f08683225cb0197fa
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.
Weakness, pattern, technique
Public exploit references
- Sign-prefixed chunk-size response-smuggling proof of conceptproof of concept · unverified
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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