CVE-2026-116267 in Mime::Parser
Summary
by MITRE • 10/28/2026
MIME::Parser versions before 5.521 for Perl allow memory exhaustion via indented error messages from a truncated, deeply nested message.
Each stored parser diagnostic is indented by three spaces per nesting level. When a message nested N levels deep ends without its closing boundaries, every level logs an error at its own depth, so the stored diagnostics grow with the square of N. The defaults place no limit on nesting depth.
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Analysis
by VulDB Data Team • 10/28/2026
The vulnerability identified in MIME::Parser versions prior to 5.521 represents a significant resource exhaustion flaw rooted in how the library handles parsing errors within deeply nested email structures. This issue is classified under CWE-400, which covers Uncontrolled Resource Consumption, and specifically manifests as a denial of service condition where an attacker can trigger memory exhaustion on the target system. The core technical flaw lies in the error logging mechanism used by the parser when it encounters malformed or truncated messages that fail to close their nested boundaries properly.
When MIME::Parser processes an email message, it tracks nesting levels to manage headers and body parts correctly. If a message is truncated such that closing tags are missing, the parser continues to attempt parsing subsequent sections as if they were still within the unclosed context of previous layers. For every level N deep where this truncation occurs, the parser generates diagnostic error messages indicating the failure to close specific MIME boundaries or headers. Crucially, each stored diagnostic is indented by three spaces for every nesting level involved in that particular error state.
This indentation strategy creates a multiplicative effect on memory usage rather than a linear one. As the depth of the nested structure increases, not only does the number of errors increase, but the size of each individual error string also grows proportionally to the current nesting depth. Consequently, if an attacker crafts a message with N levels of deep nesting that ends prematurely without proper closure, the total amount of memory consumed by these diagnostic strings scales quadratically with respect to N. This means that relatively small increases in nesting depth can lead to disproportionately large spikes in memory consumption, quickly overwhelming available system resources.
The operational impact of this vulnerability is severe for any service relying on MIME::Parser to process incoming email traffic without strict limits on message complexity or structure. Since the default configuration places no limit on nesting depth, a malicious actor can construct a specially crafted input that forces the parser into an infinite loop of error generation and memory allocation. This leads directly to application crashes, system instability, or complete denial of service as the process consumes all available RAM. In environments where MIME::Parser is used in high-throughput mail servers or web applications handling user-uploaded attachments, this flaw can be exploited remotely with minimal effort, requiring only the transmission of a single malformed message payload.
Mitigation strategies must focus on enforcing strict limits on parsing depth and implementing resource controls to prevent unbounded memory growth. The primary remediation is to upgrade MIME::Parser to version 5.521 or later, where this quadratic scaling issue has been addressed through improved handling of nested structures and error diagnostics. For systems that cannot immediately update the library, administrators should implement input validation at the application layer to reject messages with excessive nesting levels before they reach the parser. Additionally, configuring memory limits for the Perl process using operating system tools or runtime constraints can help contain the blast radius if an attack is attempted, ensuring that a single malformed message does not compromise the entire host infrastructure.