CVE-2024-49394 is a vulnerability identified in the mutt and neomutt email clients, where the In-Reply-To header field in email messages is not protected by cryptographic signing mechanisms. Typically, cryptographic signatures in email (e.g., via PGP or S/MIME) ensure the integrity and authenticity of message content, including headers. However, in this case, while the email body and other headers may be signed, the In-Reply-To header remains unsigned and thus can be manipulated by an attacker. This allows an adversary to reuse a previously signed but unencrypted email message and craft a new email that appears as a legitimate reply from the original sender. The attack does not require any privileges or user interaction, and it can be executed remotely over the network. The vulnerability impacts the integrity of email communications by enabling impersonation attacks, potentially misleading recipients about the origin of a message. There is no impact on confidentiality or availability, and no known exploits have been reported in the wild. The CVSS 3.1 base score is 5.3, reflecting a medium severity level due to the moderate impact on integrity and the ease of exploitation without authentication. No patches or fixes have been linked yet, but the issue is publicly disclosed and tracked by Red Hat and the CVE database.

For European organizations, this vulnerability poses a risk primarily to the integrity and trustworthiness of email communications. Sectors such as finance, government, legal, and critical infrastructure that rely on mutt or neomutt for secure email exchanges could be targeted for impersonation attacks, potentially leading to social engineering, fraud, or misinformation. Since the In-Reply-To header is commonly used to thread email conversations, manipulation could confuse recipients or cause misattribution of messages, undermining trust in email authenticity. Although confidentiality and availability are not affected, the ability to impersonate senders without authentication can facilitate phishing or spear-phishing campaigns. The lack of known exploits currently limits immediate risk, but the public disclosure increases the likelihood of future exploitation. Organizations using these clients in Europe should be aware of the threat, especially where email integrity is critical for operational security and compliance.

Organizations should monitor for official patches or updates from mutt and neomutt developers and apply them promptly once available. Until patches are released, administrators can implement additional email validation controls such as enforcing strict DKIM, SPF, and DMARC policies to detect and block forged emails. Users should be trained to recognize suspicious email replies that may not align with expected communication patterns. Email gateways and security appliances can be configured to flag or quarantine emails with inconsistent or suspicious In-Reply-To headers. Where possible, transitioning to email clients or systems that fully cryptographically sign all relevant headers can reduce exposure. Incident response teams should prepare to investigate potential impersonation attempts and correlate suspicious email activity with other threat intelligence. Finally, organizations should consider restricting the use of mutt and neomutt in high-risk environments until the vulnerability is resolved.