CVE-2026-123119

Description

A flaw was found in the Symfony HttpClient component. The client fails to properly pin verified IP addresses for cached hostnames across subsequent requests, causing the host to be re-resolved. A remote attacker controlling an external Domain Name System (DNS) server can exploit this behavior through DNS rebinding by returning a public IP address on the initial lookup and a private IP address on subsequent queries. This flaw enables the attacker to bypass private network restrictions and enumerate internal hosts and ports.

Statement

This vulnerability is rated as having Low impact for Red Hat products because successful exploitation requires precise DNS rebinding conditions and only permits partial network reconnaissance rather than data exfiltration or arbitrary remote code execution. Although an attacker managing authoritative nameservers can manipulate successive domain lookups to circumvent private network restrictions, the client mechanism terminates TCP sessions prior to transmitting any HTTP request payloads. Consequently, the exposure is confined to discerning host availability and open port states via differential connection errors, substantially limiting the threat to internal network discovery.

Mitigation

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Understanding the Weakness (CWE)

CWE-918

Confidentiality

Technical Impact: Read Application Data

Integrity

Technical Impact: Execute Unauthorized Code or Commands

Access Control

Technical Impact: Bypass Protection Mechanism

By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls that prevent the attackers from accessing the URLs directly. The server can be used as a proxy to conduct port scanning of hosts in internal networks, use other URLs such as that can access documents on the system (using file://), or use other protocols such as gopher:// or tftp://, which may provide greater control over the contents of requests.

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