HPE Telco Service Activator Flaw Enables Remote Access Bypass (CVE-2025-12543)

HPE released a security bulletin on February 19, 2026, warning of CVE-2025-12543 affecting Telco Service Activator. The critical flaw (CVSS 9.6) stems from improper Host header validation in the Undertow HTTP server core. Remote attackers bypass access controls via crafted HTTP requests.

The vulnerability hits versions before 10.5.0. Attackers send manipulated Host headers to evade host-based restrictions. Gateways and apps relying on header routing become vulnerable. No authentication required for remote exploitation.

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User interaction factor exists. Victims may need to follow phishing links or trigger specific client requests. Successful bypass grants unauthorized access to blocked functions. Scope changes to Cross-instance (S:C) amplify impact.

Telco Service Activator manages network services for carriers. Exposed deployments face highest risk. Attackers reach admin interfaces or service configs behind controls. Network attack vector (AV:N) enables internet reachability.

HPE rates impact as High Confidentiality, High Integrity, Low Availability. Real-world attacks target telco infrastructure frequently. Rapid patching prevents lateral movement into core networks.

Vulnerability Details Table

Host header abuse bypasses allowlists common in enterprise gateways. Attackers spoof internal hosts to reach restricted paths. Telco admins lose visibility into unauthorized access attempts.

Immediate Mitigation Steps

• Upgrade Telco Service Activator to 10.5.0 or later immediately.
• Restrict TSA interfaces to VPN/admin networks only.
• Deploy reverse proxies with strict host header validation.
• Monitor web logs for anomalous Host values and routing patterns.
• Enable WAF rules blocking Host header manipulation attempts.

Unpatched systems face active scanning. Telco environments attract nation-state actors. Patch windows close fast as exploits proliferate.

Enterprise teams report similar Undertow flaws weaponized before. HPE bulletin stresses priority for internet-facing deployments. Network segmentation buys time until upgrades complete.

Log review reveals exploitation attempts early. Unusual 4xx errors or internal host requests signal attacks. SIEM correlation spots patterns across telco assets.

Attack Requirements

No privileges needed. Network access suffices. User interaction lowers barrier via phishing. Cross-instance scope enables privilege escalation paths.

Telco operators manage millions in service configs. Breach exposes subscriber data routing and billing integration points. Containment demands swift vendor coordination.

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