CVE-2026-73494Network attack vectorHinoki check available

Authorization bypass via inconsistent HTTP request boundaries

Published Sep 14, 2026 · Updated Sep 14, 2026

HTTP request smuggling in http4s Blaze before 0.23.18 and 1.0.0-M1 through 1.0.0-M41 allows remote attackers to bypass front-end controls. BodyAndHeaderParser and Http1ServerParser accept invalid header names, obsolete folding, unsupported transfer codings, duplicate Content-Length fields, and requests carrying both Transfer-Encoding and Content-Length, producing boundaries that differ from stricter intermediaries. Exploitation requires a lenient or legacy fronting proxy that forwards the malformed request and parses its boundary differently; a default BlazeServerBuilder is exposed.

CVSS severity7.4
High
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

HTTP request smuggling in http4s Blaze before 0.23.18 and 1.0.0-M1 through 1.0.0-M41 allows remote attackers to bypass front-end controls. BodyAndHeaderParser and Http1ServerParser accept invalid header names, obsolete folding, unsupported transfer codings, duplicate Content-Length fields, and requests carrying both Transfer-Encoding and Content-Length, producing boundaries that differ from stricter intermediaries. Exploitation requires a lenient or legacy fronting proxy that forwards the malformed request and parses its boundary differently; a default BlazeServerBuilder is exposed.

The record

CVE
CVE-2026-73494
Published
Sep 14, 2026
Updated
Sep 14, 2026
Vendor
http4s
Product
http4s-blaze-server
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 14, 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.

  1. Affected versionversion=< 0.23.18

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

http4s · http4s-blaze-serverversion=< 0.23.18
http4s · Blazeversion=< 0.23.18; version=>= 1.0.0-M1, < 1.0.0-M42
http4s · blaze-httpversion=< 0.23.18; version=>= 1.0.0-M1, < 1.0.0-M42

Published CVSS scores

7.4GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
T1190Exploit Public-Facing Application

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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