CVE intelligence and bounded remediation

CVE-2023-26438 — Open-Xchange Open-Xchange Appsuite Backend security vulnerability

Medium CVSS 4.3

External service lookups for a number of protocols were vulnerable to a time-of-check/time-of-use (TOCTOU) weakness, involving the JDK DNS cache. Attackers that were timing DNS cache expiry correctly were able to inject configuration that would bypass existing network deny-lists. Attackers could exploit this weakness to discover the existence of restricted network infrastructure and service availability. Improvements were made to include deny-lists not only during the check of the provided connection data, but also during use. No publicly available exploits are known.

Severity
Medium
CVSS
4.3 (3.1)
Published
2023-08-02
CISA KEV
Not currently listed
Ecosystem
software/application
Weaknesses
CWE-918, CWE-367

Affected products

  • open-xchange / open-xchange_appsuite_backend / 7.10.6
  • open-xchange / open-xchange_appsuite_backend / 8.10.0

Matched remediation archetype

Server-side request forgery and unintended proxying

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

  • Inventory server-side URL fetchers, webhooks, importers, previews, redirects, proxies, and protocol handlers reachable from untrusted input.
  • Map egress paths to internal services, metadata endpoints, loopback, private address space, and privileged control planes.
  • Review DNS resolution, redirect, proxy, credential-forwarding, and URL parsing behavior without requesting sensitive targets.

Remediate safely

  • Replace arbitrary destinations with named integrations or a strict allowlist of schemes, hosts, ports, and paths.
  • Resolve and validate every destination and redirect hop, then enforce egress policy independently of application checks.
  • Remove ambient credentials and sensitive headers from fetchers; apply response size, time, and content limits.

Authoritative sources

Complete CVE record and remediation plan

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