Security vulnerabilities

Attached to Project: Security vulnerabilities
Opened by ciphernest7 - 01.07.2026
Last edited by cbay - 02.07.2026

Dear Alwaysdata Security Team, I hope you are doing well. I am writing to responsibly disclose a security observation identified during an assessment of your publicly accessible SMTP infrastructure. Summary During testing, multiple public-facing SMTP servers were identified exposing an Exim 4.96 SMTP banner. Based on the detected version and publicly available Exim security advisories, the affected systems may be impacted by multiple known vulnerabilities ranging from Remote Code Execution (RCE) and Privilege Escalation to Information Disclosure, SMTP Smuggling, and Denial of Service (DoS). Affected Assets IP Address Hostname Service 185.31.40.80 smtpin1.paris1.alwaysdata.com SMTP (Exim 4.96) 78.142.219.80 smtpin1.paris2.alwaysdata.com SMTP (Exim 4.96) 78.142.219.5 overlord-core.paris2.alwaysdata.com TLS Service Evidence Asset 1 IP Address: 185.31.40.80 Hostname: smtpin1.paris1.alwaysdata.com SMTP Banner 220 smtpin1.paris1.alwaysdata.com ESMTP Exim 4.96 Supported Features • STARTTLS • PIPELINING • PIPECONNECT • SMTPUTF8 • 8BITMIME Asset 2 IP Address: 78.142.219.80 Hostname: smtpin1.paris2.alwaysdata.com SMTP Banner 220 smtpin1.paris2.alwaysdata.com ESMTP Exim 4.96 Supported Features • STARTTLS • PIPELINING • PIPECONNECT • SMTPUTF8 • 8BITMIME

Asset 3 IP Address: 78.142.219.5 Hostname: overlord-core.paris2.alwaysdata.com Supported TLS Versions • TLS 1.2 • TLS 1.3 Technical Description The SMTP servers publicly disclose Exim version 4.96 through the SMTP banner. According to publicly available Exim security advisories, this version predates several security fixes released during 2023–2026. Depending on the exact build, enabled modules, and runtime configuration, the deployment may be affected by multiple security vulnerabilities. These issues include unsafe memory handling, improper input validation, authentication-related flaws, MIME parsing issues, SMTP protocol parsing weaknesses, JSON parsing bugs, UTF-8 processing vulnerabilities, and DNS handling issues. Collectively, these weaknesses increase the attack surface of the mail infrastructure and may allow attackers to compromise confidentiality, integrity, or availability under specific conditions. Potentially Applicable CVEs Critical Remote Code Execution • CVE-2023-42115 • CVE-2023-42116 • CVE-2023-42117 These vulnerabilities involve memory corruption and insufficient validation of SMTP data, potentially allowing unauthenticated remote attackers to execute arbitrary code under vulnerable configurations. Privilege Escalation • CVE-2025-30232 A use-after-free vulnerability that may allow local privilege escalation under affected deployments. Information Disclosure • CVE-2026-48840 • CVE-2026-40687 • CVE-2026-40686 • CVE-2023-42119 • CVE-2023-42114 These vulnerabilities may expose process memory, heap contents, or sensitive information through malformed protocol interactions. Memory Corruption • CVE-2026-40685 • CVE-2025-67896 These issues involve heap corruption or out-of-bounds memory operations that may lead to crashes or code execution depending on the deployment. SMTP Security Issues • CVE-2023-51766 (SMTP Smuggling) • CVE-2024-39929 (RFC2231 MIME Parsing) These vulnerabilities may enable email spoofing, bypass of SPF-related protections, or delivery of blocked attachments under specific mail flow configurations. Denial of Service • CVE-2026-40684 • CVE-2022-3620 • CVE-2022-3559 These vulnerabilities may allow attackers to trigger service crashes or otherwise reduce SMTP service availability. Security Impact If the affected version is confirmed and the vulnerable functionality is enabled, successful exploitation could potentially result in: • Remote Code Execution (RCE) • SMTP Server Compromise • Privilege Escalation • Information Disclosure • Heap or Stack Memory Corruption • SMTP Smuggling • Email Spoofing • SPF Protection Bypass • Delivery of Malicious Attachments • Denial of Service (DoS) The actual impact depends on the deployed Exim configuration and whether the relevant vulnerable components are enabled. Recommendation I recommend the following remediation steps:

Upgrade Exim to the latest supported stable release.
Apply all vendor security patches.
Verify that the SMTP servers are no longer exposing outdated Exim versions.
Review enabled authentication mechanisms and optional Exim modules.
Validate that all publicly disclosed Exim vulnerabilities affecting the deployed version have been remediated.
Perform a post-upgrade security verification to ensure the service is no longer affected. Conclusion The observed SMTP infrastructure publicly identifies itself as running Exim 4.96, a version associated with multiple publicly disclosed security vulnerabilities. While additional validation is required to determine which vulnerabilities are exploitable in your specific environment, upgrading to the latest supported release is strongly recommended to reduce the attack surface and maintain a secure mail infrastructure. This report is submitted in the spirit of responsible disclosure. I would be happy to provide any additional information if required. Kind regards, Cyber_Subhash Security Researcher