Exim — CraftedSignal Threat Feedhttps://feed.craftedsignal.io/vendors/exim/Trending threats, MITRE ATT&CK coverage, and detection metadata — refreshed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioThu, 30 Apr 2026 00:00:00 +0000Multiple Vulnerabilities in Exim Mail Transfer Agenthttps://feed.craftedsignal.io/briefs/2026-04-exim-vulns/Thu, 30 Apr 2026 00:00:00 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-04-exim-vulns/Multiple vulnerabilities in Exim versions prior to 4.99.2 allow an attacker to cause a remote denial of service, a breach of data confidentiality, and an unspecified security problem.On April 30, 2026, CERT-FR published an advisory regarding multiple vulnerabilities affecting Exim versions prior to 4.99.2. These vulnerabilities could allow a remote attacker to perform a denial-of-service attack, achieve unauthorized data access, or cause other unspecified security impacts. The vulnerabilities are detailed in the Exim security bulletin cve-2026-04.1. Due to the widespread use of Exim as a mail transfer agent (MTA), these vulnerabilities pose a significant risk to organizations that have not yet applied the necessary patches. Successful exploitation can disrupt email services and potentially lead to sensitive information disclosure.

Attack Chain

  1. Attacker identifies an Exim server running a vulnerable version (prior to 4.99.2).
  2. The attacker crafts a malicious network packet targeting a specific vulnerability, such as CVE-2026-40684, CVE-2026-40685, CVE-2026-40686, or CVE-2026-40687.
  3. The attacker sends the crafted packet to the vulnerable Exim server via SMTP.
  4. The Exim process receives the malicious packet and processes it due to missing or insufficient input validation.
  5. Depending on the exploited vulnerability, this could lead to a denial-of-service condition by crashing the Exim process.
  6. Alternatively, successful exploitation may lead to an information leak by disclosing sensitive data from Exim’s memory.
  7. In other cases, the unspecified security issue could grant further access to the underlying system, depending on the nature of vulnerability.
  8. The attacker exploits this access to achieve goals like data exfiltration or further system compromise (depending on the specific vulnerability triggered).

Impact

Successful exploitation of these vulnerabilities could lead to denial-of-service conditions, preventing legitimate users from sending and receiving emails. Data confidentiality could also be compromised if sensitive information is exposed. The advisory does not specify the number of victims or specific sectors targeted, but given the widespread use of Exim, a large number of organizations could be affected. Failure to patch Exim servers could result in significant disruption of email services and potential data breaches.

Recommendation

  • Immediately upgrade Exim servers to version 4.99.2 or later to remediate the vulnerabilities mentioned in the Exim security bulletin cve-2026-04.1.
  • Monitor network traffic for suspicious activity targeting Exim servers, and correlate with the known CVEs (CVE-2026-40684, CVE-2026-40685, CVE-2026-40686, CVE-2026-40687).
  • Implement rate limiting and connection filtering to mitigate potential denial-of-service attacks against Exim servers.
  • Deploy a web server rule that monitors for requests matching known attack patterns related to Exim vulnerabilities.
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