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GHSA-crq5-92j2-j7wv

MediumCVSS 5.9 / 10
Published Sep 15, 2026·Last modified Sep 15, 2026
Affected Components(5)
Maven logoorg.http4s/http4s-server_2.13
< 0.23.35
Maven logoorg.http4s/http4s-server_2.12
< 0.23.35
Maven logoorg.http4s/http4s-server_2.13
1.0.0-M1 – 1.0.0-M47
1 / 2
Description

The static content handlers ResourceService and WebjarService URL decode each path segment and then reject only segments that are exactly "", ".", or "..". A percent-encoded separator (%2F) lets an attacker smuggle a ../ segment past that filter and escape the configured base, reading resources that should not be public.

On Windows, a similar attack exists with (%5C).

Impact

Disclosure of classpath or webjar resources outside the configured base.

Preconditions

  • Application uses ResourceService (with a non-root base path) or WebjarService
  • At least one classpath entry is served from a directory (e.g. sbt run, exploded .war)
  • Backend forwards %2F/%5C without normalizing (e.g., Ember, Blaze)

Fixes

The patch rejects any decoded path segment containing / (%2F) or \ (%5C) with a 400 Bad Request in ResourceService and WebjarService.

FileService was not exploitable, but the same guards are applied for consistency and to remove its reliance on path normalization.

Workarounds

  • Deploy as a fat jar, with no filesystem directories on the classpath.
  • Front the service with a proxy that rejects/normalizes %2F and %5C in the request path.
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Risk Scores
Base Score
5.9

The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information.

Threat Intelligence
5.4

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.76%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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