CVE-2007-1713 in BASP21
Summary
by MITRE
CRLF injection vulnerability in BSMTP.DLL in B21Soft BASP21 2003.0211, and BASP21 Pro 1.0.702.27 and earlier, allows remote attackers to inject arbitrary headers into e-mail messages via CRLF sequences in Subject lines.
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Analysis
by VulDB Data Team • 08/27/2018
The CVE-2007-1713 vulnerability represents a critical cross-site scripting and email header injection flaw discovered in B21Soft BASP21 email server software versions 2003.0211 and earlier. This vulnerability specifically affects the BSMTP.DLL component within the BASP21 email server infrastructure, creating a pathway for remote attackers to manipulate email message headers through carefully crafted CRLF (Carriage Return Line Feed) sequences embedded in subject lines. The flaw stems from insufficient input validation and sanitization mechanisms within the email processing pipeline, allowing malicious actors to inject arbitrary email headers that can be interpreted by email clients and servers during message transmission. This vulnerability directly maps to CWE-113, which describes improper neutralization of CRLF sequences in HTTP headers, and extends to broader email security concerns related to header injection attacks. The attack vector operates through the manipulation of standard email protocols where CRLF characters are used to separate message headers from the message body, making this a fundamental protocol-level vulnerability.
The technical exploitation of this vulnerability occurs when an attacker submits an email message containing CRLF sequences within the subject line field. These sequences, typically represented as %0D%0A or \r\n in encoded formats, are processed by the vulnerable BSMTP.DLL component without proper sanitization. When the email server processes these malformed subject lines, it inadvertently incorporates the injected CRLF sequences into the email header structure, allowing attackers to insert additional headers such as From, To, Reply-To, or even Content-Type fields. This header injection capability enables a range of malicious activities including email spoofing, phishing attacks, and potential redirection of email traffic. The vulnerability's impact extends beyond simple header manipulation as it can be leveraged to bypass email filtering systems, manipulate email routing, and create confusion in email client processing. The flaw is particularly dangerous because it operates at the email server level, affecting all email messages processed through the vulnerable system regardless of the sender or recipient.
The operational impact of this vulnerability creates significant security risks for organizations relying on the affected BASP21 email server software. Attackers can exploit this weakness to send phishing emails that appear to originate from legitimate sources, manipulate email delivery routing, or even inject malicious content into email headers that could trigger security alerts or bypass spam filters. The vulnerability undermines the integrity of email communications by allowing unauthorized modification of email metadata, potentially leading to reputation damage for the affected organization. Email security systems that depend on header validation may be bypassed, creating false positives or negatives in threat detection. From an attacker's perspective, this vulnerability provides a straightforward method for conducting email-based social engineering attacks without requiring complex exploitation techniques, making it particularly attractive for threat actors. The vulnerability also affects email server logging and monitoring capabilities, as injected headers can obscure the true origin and content of malicious emails, complicating forensic analysis and incident response efforts.
Organizations should implement immediate mitigations including upgrading to patched versions of B21Soft BASP21 software, implementing strict input validation for all email subject fields, and deploying email header filtering mechanisms to detect and block CRLF injection attempts. Network segmentation and email server hardening practices should be enhanced to reduce the attack surface, while monitoring systems should be configured to detect unusual header patterns in email traffic. Security teams should also consider implementing email authentication mechanisms such as SPF, DKIM, and DMARC to provide additional layers of protection against header injection attacks. The vulnerability highlights the importance of input validation in email processing systems and demonstrates how protocol-level flaws can have cascading effects on overall email security infrastructure. Organizations using legacy email server software should conduct comprehensive security assessments to identify similar vulnerabilities in their email infrastructure, as this type of injection vulnerability often indicates broader security gaps in email processing components. This vulnerability also underscores the need for regular security updates and patch management processes to prevent exploitation of known weaknesses in email server software.