CVE-2026-66746Public exploitNetwork attack vector

Response splitting via unvalidated header values

Published Jul 28, 2026 · Updated Jul 28, 2026

HTTP response splitting in tomaka Rouille 0.4.0 through 3.6.2 allows remote attackers to inject headers through crafted input. Server::process passes response header values to tiny_http after only an ASCII check, while Request::get_param percent-decodes CRLF and session::session copies a client Cookie value into Set-Cookie. Exploitation requires an application to reflect request-derived text into a response header or use the session helper; a victim link or shared cache can turn the primitive into cache poisoning, session fixation, or security-header override.

CVSS severity5.3
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP response splitting in tomaka Rouille 0.4.0 through 3.6.2 allows remote attackers to inject headers through crafted input. Server::process passes response header values to tiny_http after only an ASCII check, while Request::get_param percent-decodes CRLF and session::session copies a client Cookie value into Set-Cookie. Exploitation requires an application to reflect request-derived text into a response header or use the session helper; a victim link or shared cache can turn the primitive into cache poisoning, session fixation, or security-header override.

The record

CVE
CVE-2026-66746
Published
Jul 28, 2026
Updated
Jul 28, 2026
Vendor
tomaka
Product
Rouille
Classifications
CWE-113, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 28, 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=0.4.0 <=3.6.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

tomaka · Rouilleversion=0.4.0 <=3.6.2

Published CVSS scores

5.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
5.4VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/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 exploitPublished

Weakness, pattern, technique

CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
T1190Exploit Public-Facing Application

Public exploit references

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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