# CVE-2026-100725: http4k cookie storage domain scoping bypass

Source: https://junglewise.ai/threats/cve-2026-100725-http4k-maven-artifact-org-http4k-http4k-core-before-6-48-0-0-5  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-27. Updated: 2026-09-27  
License: CC BY 4.0 with a link back

CVE-2026-100725 · Severity: medium · CVSS 6.5 · Published 2026-09-27

http4k is a Kotlin HTTP client library used for making web requests. When a single cookie storage instance handles requests to multiple websites or uses both secure and plain HTTP connections, cookies intended for one site can leak to others, or sensitive session cookies marked "secure" can be transmitted over unencrypted connections. This could allow attackers to intercept authentication credentials or impersonate legitimate users.

Technologies: [Http4k-Core](https://junglewise.ai/threats/technologies/http4k-core). Vendors: [Http4k](https://junglewise.ai/threats/vendors/http4k).

## Quick answers

**Is CVE-2026-100725 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-100725 being exploited in the wild.

**How severe is CVE-2026-100725?** Medium severity, with a CVSS score of 6.5, published 27 September 2026.

**Which products and versions are affected?** Http4k-Core before 6.48.0.0, 5.42.0.0, and 4.51.0.0.

**Is there a fix for CVE-2026-100725?** A patch was published on 2026-06-16: v6.48.0.0, v5.42.0.0, v4.51.0.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-100725 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-100725?** Check whether you run Http4k-Core at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The BasicCookieStorage component fails to enforce RFC 6265 cookie scoping rules for domain, path, and Secure attributes. An attacker can exploit this by reusing a single storage instance across multiple origins or schemes to extract cookies set for one origin and send them to another, or force secure cookies over plaintext HTTP. The vulnerability requires use of BasicCookieStorage with multiple origins; single-origin deployments are unaffected. Patched versions introduce RFC 6265-compliant DefaultCookieStorage as the new default.

## Affected products

- http4k http4k-core before 6.48.0.0, 5.42.0.0, and 4.51.0.0

## Timeline

- 2026-09-27: disclosed
- 2026-06-16: patched: v6.48.0.0, v5.42.0.0, v4.51.0.0

## References

- [https://github.com/http4k/http4k/commit/6a9b44d743](https://github.com/http4k/http4k/commit/6a9b44d743)
- [https://github.com/http4k/http4k/security/advisories/GHSA-pr33-38xx-6r26](https://github.com/http4k/http4k/security/advisories/GHSA-pr33-38xx-6r26)

## Related threats

- [http4k reverse proxy host header substring matching bypass](https://junglewise.ai/threats/cve-2026-100724-http4k-maven-package-org-http4k-http4k-core-before-6-49-0-0-5-42)
- [http4k unbounded gzip decompression denial of service](https://junglewise.ai/threats/cve-2026-53659-http4k-unbounded-gzip-decompression-denial-of-service)
- [http4k information exposure via improper cookie scoping in BasicCookieStorage](https://junglewise.ai/threats/http4k-information-exposure-via-improper-cookie-scoping-in-24a5c491)
- [http4k misleading HmacSha256.hash naming leads to unkeyed digest usage](https://junglewise.ai/threats/http4k-misleading-hmacsha256-hash-naming-leads-to-unkeyed-digest-usage-d5026b8c)
- [http4k auth bypass via loose Host matching in reverseProxy](https://junglewise.ai/threats/http4k-auth-bypass-via-loose-host-matching-in-reverseproxy-bcd046a3)