CVE-2026-69201: Http4s: ResourceService and Webjar Service path escape via percent-encoded separators
Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, ResourceService and WebjarService decode each URL path segment but reject only segments exactly equal to an empty string, a dot, or two dots. A request containing percent-encoded slash or backslash separators can turn an accepted segment into a parent-directory traversal after decoding, allowing access to classpath or WebJar resources outside the configured base when a directory-backed classpath is served and the backend preserves the encoded separator. The patch rejects decoded segments containing slash or backslash in ResourceService and WebjarService, and applies the same guard to the non-exploitable FileService for consistency. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
http4sto a version that resolves this vulnerability.Fixed in 0.23.35 - Upgrade
Upgrade
http4sto a version that resolves this vulnerability.Fixed in 1.0.0-M47
Event History
Frequently Asked Questions
Which deployments are realistically exposed?
ResourceService and WebjarService deployments are exposed when they serve a directory-backed classpath and the backend preserves percent-encoded slash or backslash separators. FileService received the same validation guard for consistency, but is described as non-exploitable.
What does an attacker need to exploit this issue?
An attacker can send a crafted HTTP request; no privileges or user interaction are required. Exploitation depends on using percent-encoded slash or backslash characters in a path segment and on the affected backend behavior.
What is the impact if exploitation succeeds?
The issue can allow access to classpath or WebJar resources outside the configured base directory. The stated impact is confidentiality only; integrity and availability are not affected.
What remediation is available?
Upgrade to Http4s 0.23.35 or 1.0.0-M47. These versions reject decoded ResourceService and WebjarService path segments that contain slash or backslash characters.