CVE-2019-11049 in PHP
Summary
by MITRE
In PHP versions 7.3.x below 7.3.13 and 7.4.0 on Windows, when supplying custom headers to mail() function, due to mistake introduced in commit 78f4b4a2dcf92ddbccea1bb95f8390a18ac3342e, if the header is supplied in lowercase, this can result in double-freeing certain memory locations.
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Analysis
by VulDB Data Team • 08/17/2026
The vulnerability CVE-2019-11049 represents a critical memory corruption issue affecting PHP versions 7.3.x below 7.3.13 and 7.4.0 on Windows operating systems. This flaw specifically targets the mail() function implementation within PHP's Windows environment, where improper handling of custom headers leads to dangerous memory management behavior. The vulnerability was introduced through a specific code commit that altered how header processing occurs, creating a condition where memory allocation and deallocation sequences become corrupted. The issue manifests when custom email headers are provided to the mail() function with lowercase naming conventions, which triggers an unexpected code path in the underlying memory management system.
The technical root cause of this vulnerability lies in a double-free memory error that occurs during header processing within PHP's mail() function implementation. When lowercase headers are passed to the function, the modified code path executes a sequence where memory locations are freed twice, leading to undefined behavior and potential exploitation. This memory corruption vulnerability falls under the CWE-415 category of double free conditions, where the same memory block is deallocated multiple times, causing heap corruption that can be leveraged by attackers to execute arbitrary code. The specific commit 78f4b4a2dcf92ddbccea1bb95f8390a18ac3342e introduced this flaw by altering the header processing logic without proper consideration of the memory deallocation sequence, particularly affecting Windows implementations where the memory management differs from Unix-like systems.
The operational impact of CVE-2019-11049 extends beyond simple memory corruption, as it creates potential for remote code execution when exploited through web applications that utilize the mail() function with user-supplied headers. Attackers can craft malicious header values that trigger the double-free condition, potentially leading to arbitrary code execution on vulnerable systems. This vulnerability is particularly concerning in web server environments where PHP applications process user input through email headers, as it can be exploited through various attack vectors including web-based applications, email processing scripts, and any system that relies on the mail() function with custom header parameters. The Windows-specific nature of this vulnerability means that it primarily affects PHP installations running on Microsoft Windows platforms, though the underlying memory corruption principles make it applicable to similar implementations across different operating systems. The vulnerability operates at the application level, requiring no special privileges to exploit and can be triggered through standard web application requests.
Mitigation strategies for CVE-2019-11049 focus primarily on immediate version updates to PHP 7.3.13 or PHP 7.4.0, which contain the necessary code fixes to prevent the double-free condition from occurring. Organizations should prioritize patching their PHP installations and thoroughly test updates in staging environments before deployment to ensure compatibility with existing applications. Additional defensive measures include implementing strict input validation for email headers, sanitizing all user-supplied header values before passing them to the mail() function, and monitoring for unusual memory allocation patterns in PHP processes. Security teams should also consider implementing network-based intrusion detection systems that can identify suspicious header patterns commonly associated with this vulnerability. The ATT&CK framework categorizes this vulnerability under T1059.007 for scripting and T1566 for phishing, as exploitation often occurs through web-based attacks targeting vulnerable PHP applications. Organizations should also implement proper application firewall rules to restrict access to vulnerable endpoints and consider using PHP hardening techniques such as disabling unnecessary functions and implementing proper error handling to prevent exploitation attempts.