CVE-2007-1717 in PHP
Summary
by MITRE
The mail function in PHP 4.0.0 through 4.4.6 and 5.0.0 through 5.2.1 truncates e-mail messages at the first ASCIIZ ( \0 ) byte, which might allow context-dependent attackers to prevent intended information from being delivered in e-mail messages. NOTE: this issue might be security-relevant in cases when the trailing contents of e-mail messages are important, such as logging information or if the message is expected to be well-formed.
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Analysis
by VulDB Data Team • 04/25/2025
The vulnerability described in CVE-2007-1717 represents a critical flaw in PHP's mail function implementation that affects versions ranging from 4.0.0 through 4.4.6 and 5.0.0 through 5.2.1. This issue stems from improper handling of null byte characters within email message content, specifically truncating messages at the first occurrence of an ASCII null character. The vulnerability operates at the core level of PHP's mail functionality, where the underlying sendmail or mail system processes email content through a buffer that terminates processing when encountering the null byte. This behavior violates fundamental email protocol standards and can lead to partial message delivery, creating significant security implications for applications relying on complete message transmission. The flaw is classified under CWE-128 as "Wrap-around Error" and specifically relates to improper handling of null terminators in string processing, making it a classic buffer overflow vulnerability in the context of email handling.
The technical exploitation of this vulnerability occurs when PHP applications generate email messages containing null bytes within their content, either through user input manipulation or internal application logic. When the mail function processes such messages, it terminates the email transmission at the first null byte encountered, effectively corrupting the message content and potentially stripping away critical information. This truncation behavior is particularly dangerous because it can silently remove important data such as log entries, authentication tokens, or structured information that forms the complete message payload. The vulnerability demonstrates a clear violation of the principle of least privilege and data integrity, as legitimate message content is altered without proper validation or error handling. From an operational perspective, this flaw can be leveraged by attackers to craft malicious email payloads that bypass content filtering systems or to silently remove sensitive information from messages, creating a vector for information leakage or denial of service attacks.
The operational impact of CVE-2007-1717 extends beyond simple message corruption to potentially enable more sophisticated attacks depending on the application context. In logging scenarios, where applications use PHP mail functions to send log information, attackers could manipulate input to truncate messages at critical points, effectively hiding malicious activities from administrators. The vulnerability aligns with ATT&CK technique T1070.004 for "Indicator Removal on Host" by enabling attackers to manipulate email content to remove evidence of their activities. Applications using PHP mail functions for security notifications, password reset emails, or system alerts become particularly vulnerable when they contain structured data or authentication tokens that could be truncated. The security implications are further compounded when considering that this vulnerability can be exploited through user-supplied input, making it a common vector for injection attacks. Organizations relying on PHP-based applications for email communication face significant risk of data loss, security bypasses, or information disclosure when this vulnerability remains unpatched.
Mitigation strategies for CVE-2007-1717 require immediate patching of affected PHP versions to the latest stable releases that address the null byte handling issue. System administrators should implement comprehensive input validation and sanitization routines to prevent null byte injection in email content, particularly for user-supplied data. The recommended approach involves implementing strict content filtering that removes or encodes null bytes from email message bodies before processing through PHP's mail function. Organizations should also consider migrating to more secure email handling libraries such as PHPMailer or SwiftMailer, which properly handle null bytes and provide better security features than the native mail function. Network-level protections can include implementing email content filtering that identifies and blocks messages containing null bytes, though this approach is less effective than addressing the root cause. Security monitoring should include detection of unusual email truncation patterns or message corruption that could indicate exploitation attempts. The vulnerability serves as a reminder of the importance of proper string handling in security-critical functions and the necessity of thorough testing for null byte handling in application code. Regular security audits and code reviews should specifically target email handling components to identify similar vulnerabilities in custom implementations.