CVE-2026-66746

Rouille 0.4.0 through 3.6.2 contains an HTTP response splitting vulnerability that allows remote attackers to inject arbitrary response headers by embedding carriage return (0x0D) or line feed (0x0A) bytes into attacker-controlled input. Attackers can exploit percent-decoded query parameters reflected into response headers or inject bare LF characters into Cookie header values that are interpolated directly into Set-Cookie response headers, enabling cache poisoning, session fixation, and security header override attacks such as bypassing CSP or CORS policies.

CVSS v4.0

5.3 MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS v3.1

5.4 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

EPSS

0.24% chance of exploitation in the next 30 days, 15th percentile

Published

2026-07-28

Updated

2026-07-29

Proof-of-concept exploits (1)

• theopaid/HTTP-Response-Splitting-via-Unvalidated-Response-Header-Values-rouille-0★ · 2026-07-28

References

• CVE Record
• NVD entry

Related

• CVE-2023-27163
• CVE-2026-66729
• CVE-2026-66730
• CVE-2026-66731
• CVE-2026-66748
• CVE-2026-66750