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CVE-2026-85181 – Authentication Bypass / Admin Session Forgery – Dianping CAT ≤ 3.1.0

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Summary

CVE-2026-85181 is a critical authentication bypass vulnerability in Dianping’s CAT (a Java-based application performance monitoring platform), rated 9.8 (CVSS v3.1). The flaw allows an unauthenticated network attacker to forge a valid administrator session cookie entirely offline, because CAT’s session integrity check relies solely on Java’s unkeyed String.hashCode() function combined with a client-controlled X-Forwarded-For header used for IP validation. Successful exploitation grants full administrative access to CAT’s configuration console with no prior authentication or user interaction required.

Technical details

  • Root cause: CAT’s TokenBuilder.java computes the session cookie checksum using getCheckSum(), which is based on Java’s String.hashCode() — a public, deterministic, non-cryptographic hash with no server-side secret key (CWE-565: Reliance on Cookies without Validation and Integrity Checking).
  • Compounding flaw: The parse() method in TokenBuilder.java validates the session against a client-IP value, and HttpUtils.java‘s getRemoteAddress() derives that IP directly from the attacker-controllable X-Forwarded-For HTTP header rather than the true socket-level remote address.
  • Trigger conditions: An attacker can compute a valid checksum offline for an arbitrary username/timestamp/IP payload (since hashCode() is a known, reproducible algorithm), then submit a forged session cookie along with a matching spoofed X-Forwarded-For header to bypass IP-based validation.
  • Attack vector: Network-based (AV:N), no privileges or user interaction required, low attack complexity.
  • Impact: Full compromise of confidentiality, integrity, and availability — an attacker can create an unauthorized, fully privileged admin session and access CAT’s configuration management functionality without valid credentials.

Affected software

  • Vendor/Product: Dianping CAT (com.dianping.cat/parent Maven package)
  • Versions affected: All versions from the initial release through 3.1.0
  • Fixed: All versions released after 3.1.0 are not affected

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • (A CVSS v4.0 score of 9.3, Critical, is also recorded: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N)

Mitigation and recommended actions

  • Immediate: Upgrade Dianping CAT to a version released after 3.1.0, where this issue has been resolved.
  • If no patch can be applied immediately:
    • Do not expose CAT’s admin console or session-handling endpoints directly to untrusted networks; restrict access via firewall/VPN to trusted administrative hosts only.
    • Strip or ignore client-supplied X-Forwarded-For headers at the load balancer/reverse proxy layer unless the proxy chain is fully trusted and configured to overwrite (not append to) this header.
    • Monitor for anomalous admin session creation events and unexpected X-Forwarded-For values in access logs.
    • Where feasible, disable or restrict access to CAT’s configuration/admin interface until patched.

References

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