CVE-2019-11703 in Thunderbird
Summary
by MITRE
A flaw in Thunderbird's implementation of iCal causes a heap buffer overflow in parser_get_next_char when processing certain email messages, resulting in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.7.1.
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Analysis
by VulDB Data Team • 03/09/2025
The vulnerability identified as CVE-2019-11703 represents a critical heap buffer overflow flaw within Mozilla Thunderbird's iCalendar processing functionality. This issue manifests specifically within the parser_get_next_char function, which is responsible for parsing calendar data embedded in email messages. The vulnerability arises from insufficient bounds checking when handling malformed iCalendar data structures, creating a condition where an attacker can craft specially formatted calendar attachments that trigger memory corruption during message processing.
The technical exploitation of this vulnerability occurs when Thunderbird attempts to parse malicious iCalendar data contained within email messages. The parser_get_next_char function fails to validate buffer boundaries before reading character data from the calendar payload, allowing an attacker to overflow a heap-allocated buffer. This heap overflow condition can lead to arbitrary code execution if carefully crafted, as the corrupted memory can be manipulated to redirect program execution flow. The vulnerability is particularly dangerous because it operates within the email client's message parsing pipeline, meaning that simply opening or previewing an affected email message could trigger the exploit without requiring user interaction beyond normal email processing.
From an operational perspective, this vulnerability affects Thunderbird versions prior to 60.7.1, making it a significant concern for organizations that have not yet updated their email clients. The attack vector is particularly insidious because it can be delivered through standard email channels, requiring no specialized knowledge of the target system beyond the ability to send email messages. The vulnerability aligns with CWE-121, heap-based buffer overflow, and can be mapped to ATT&CK technique T1204.002 for social engineering through email. Organizations running affected versions of Thunderbird face potential compromise risks when users process emails containing malicious calendar attachments, as the exploit can be triggered automatically during message preview or even during normal background processing of calendar data.
The mitigation strategy for CVE-2019-11703 requires immediate deployment of Thunderbird version 60.7.1 or later, which contains the necessary patches to address the buffer overflow condition. Security administrators should implement comprehensive email filtering policies to block calendar attachments from untrusted sources and consider deploying sandboxing solutions around email processing to limit potential impact. Additionally, user education regarding the dangers of opening calendar attachments from unknown senders remains crucial, as this vulnerability can be exploited through social engineering approaches. The fix addresses the root cause by implementing proper bounds checking in the parser_get_next_char function, ensuring that all memory access operations are validated against buffer boundaries before execution. Organizations should also conduct vulnerability assessments to identify any systems running older versions of Thunderbird and prioritize patch deployment across all endpoints to prevent exploitation attempts.