CVE-2026-74882 in openssl_encrypt
Summary
by MITRE • 08/17/2026
openssl_encrypt versions before 1.4.0 contain an insecure default configuration that trusts the entire RFC 1918 private address space in IntegrityProxyConfig trusted_proxies. Attackers on private networks can forge client certificate headers to bypass mTLS authentication when ProxyAuth validation is relaxed or modified.
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Analysis
by VulDB Data Team • 08/17/2026
The vulnerability identified in OpenSSL Encrypt versions prior to 1.4.0 stems from an insecure default configuration within the IntegrityProxyConfig component, specifically regarding how trusted proxies are defined for mutual Transport Layer Security authentication contexts. The core technical flaw lies in the overly permissive scope of the trusted_proxies parameter, which by default trusts the entire RFC 1918 private address space rather than a specific list of known and verified proxy servers or load balancers. This configuration error creates a significant gap in network-level trust boundaries, allowing any device operating within standard private IP ranges to be treated as an authorized intermediary for client certificate validation processes.
From a technical perspective, this misconfiguration directly impacts the integrity checks performed during mutual authentication flows where ProxyAuth is utilized. In typical deployments involving reverse proxies or API gateways, these intermediaries often modify HTTP headers such as X-Forwarded-For or custom header fields containing client certificates to pass identity information upstream to backend services. When the system trusts all private addresses indiscriminately, an attacker positioned on a local network segment can intercept traffic and inject forged client certificate headers into requests directed at the protected service. Because the application validates these proxies based solely on their IP address falling within the broad RFC 1918 range, it accepts the spoofed identity without verifying whether the request actually originated from a legitimate proxy infrastructure component designated by the administrator.
The operational impact of this vulnerability is severe, primarily resulting in authentication bypass and unauthorized access to protected resources. Attackers who have gained any level of network connectivity within private networks can exploit this flaw to impersonate authenticated users or services that rely on client certificates for identity assertion. This undermines the fundamental security guarantees provided by mutual TLS, which is designed to ensure both server and client authenticity through cryptographic verification. By bypassing these checks, attackers may gain access to sensitive data, perform actions with elevated privileges, or pivot further into internal network segments under the guise of a trusted entity. The risk is particularly acute in environments where ProxyAuth validation rules are relaxed or modified to accommodate complex routing topologies without corresponding strict IP whitelisting controls.
This vulnerability aligns closely with CWE-287 Improper Authentication and CWE-918 Server-Side Request Forgery, as it involves the misuse of trust relationships within network architecture to bypass security mechanisms. In terms of MITRE ATT&CK mapping, this behavior corresponds to T1046 Network Service Discovery combined with techniques for credential spoofing or header injection, allowing adversaries to masquerade as legitimate internal services. The exploitation relies on lateral movement capabilities and the ability to manipulate HTTP headers during transit between network segments.
To mitigate this risk, organizations must immediately update OpenSSL Encrypt to version 1.4.0 or later where these default configurations have been hardened. For environments unable to upgrade promptly, administrators should manually override the trusted_proxies configuration in IntegrityProxyConfig to explicitly list only the specific IP addresses of authorized proxy servers and load balancers rather than relying on broad private address ranges. Implementing strict network segmentation policies that limit access to authentication endpoints can also reduce the attack surface by preventing unauthorized devices from reaching the vulnerable services. Additionally, deploying intrusion detection systems capable of identifying anomalous header injection patterns or unexpected source IPs for authenticated sessions provides an additional layer of defense against exploitation attempts targeting this configuration weakness.