CVE-2018-5161 in Firefox ESR
Summary
by MITRE
Crafted message headers can cause a Thunderbird process to hang on receiving the message. This vulnerability affects Thunderbird ESR < 52.8 and Thunderbird < 52.8.
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Analysis
by VulDB Data Team • 03/22/2023
This vulnerability resides in the email client Thunderbird and represents a denial of service condition that occurs when processing specially crafted message headers. The flaw allows an attacker to construct email messages with malformed headers that cause Thunderbird to enter an infinite loop or indefinite hang state during message processing. This behavior affects both Thunderbird ESR versions prior to 52.8 and standard Thunderbird versions before 52.8, indicating it was a widespread issue across the product line during that time period. The vulnerability specifically targets the message parsing mechanism within Thunderbird's email handling infrastructure, where the client fails to properly validate or sanitize incoming header data.
The technical implementation of this vulnerability involves the manipulation of email header fields in a manner that triggers unexpected behavior in Thunderbird's parsing logic. When the email client attempts to process these malformed headers, it encounters a condition that causes the application to become unresponsive or consume excessive CPU resources while trying to parse the malformed data. This type of vulnerability falls under the category of resource exhaustion attacks, where the attacker can force the application into a state where it becomes non-responsive to legitimate user input or other incoming messages. The behavior typically manifests as the application hanging during message retrieval or display operations, requiring manual intervention to restore normal functionality.
From an operational impact perspective, this vulnerability presents significant risks to organizations relying on Thunderbird for email communication. The denial of service condition can disrupt normal email workflows and potentially be exploited in targeted attacks against specific users or systems. An attacker could send a single malicious email to a victim's Thunderbird client, causing it to hang and potentially preventing the user from accessing their email inbox or receiving legitimate messages. This vulnerability is particularly concerning in enterprise environments where email availability is critical for business operations. The impact extends beyond simple inconvenience as it can be used to disrupt communication channels or serve as a stepping stone for more sophisticated attacks.
The vulnerability demonstrates a classic lack of proper input validation and sanitization within Thunderbird's email processing pipeline, which aligns with common weakness patterns identified in the CWE database. This issue can be categorized as a weakness in input validation, specifically related to improper handling of malformed data during parsing operations. The ATT&CK framework would classify this vulnerability under the technique of "Resource Exhaustion" or potentially "Execution Guardrails" where an attacker manipulates application behavior to consume excessive resources. Security practitioners should note that this vulnerability represents a fundamental flaw in the email client's robustness against malformed input, highlighting the importance of defensive programming practices. The issue also underscores the need for proper error handling and timeout mechanisms in email processing applications. Organizations should implement immediate mitigations including updating to Thunderbird versions 52.8 or later, where this vulnerability has been addressed through improved header parsing validation. Additionally, email administrators should consider implementing additional filtering mechanisms at network boundaries to detect and block suspicious email headers before they reach client systems, as a defensive measure against potential exploitation of this vulnerability.