CVE-2017-5447 in Firefox
Summary
by MITRE
An out-of-bounds read during the processing of glyph widths during text layout. This results in a potentially exploitable crash and could allow an attacker to read otherwise inaccessible memory. This vulnerability affects Thunderbird < 52.1, Firefox ESR < 45.9, Firefox ESR < 52.1, and Firefox < 53.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a critical out-of-bounds read condition that occurs during text layout processing within Mozilla's rendering engine. The flaw manifests when the application processes glyph widths during text rendering operations, specifically affecting how font metrics are calculated and stored in memory. The vulnerability stems from insufficient bounds checking in the text layout algorithm that handles character width calculations, allowing an attacker to manipulate input data that triggers memory access beyond allocated buffer boundaries. This type of vulnerability falls under the CWE-125 category of out-of-bounds read conditions, which are particularly dangerous because they can lead to information disclosure and potentially remote code execution when combined with other exploit primitives. The affected software versions include Thunderbird versions prior to 52.1, Firefox ESR versions prior to 45.9 and 52.1, and Firefox versions prior to 53, indicating this was a widespread issue affecting multiple Mozilla products.
The operational impact of this vulnerability is significant as it can be exploited through maliciously crafted web content or email messages containing specially formatted text. When an attacker successfully triggers this out-of-bounds read, the application crashes due to memory corruption, but more critically, the flaw allows for memory disclosure attacks where adjacent memory regions can be read by the malicious code. This memory disclosure capability is particularly concerning because it can expose sensitive information such as stack canaries, heap metadata, or cryptographic keys that may be stored in adjacent memory locations. The vulnerability operates at the application level rather than at the system level, making it a prime candidate for exploitation in browser-based attack scenarios where the attacker can leverage the crash to gain additional information about memory layout for more sophisticated attacks.
The exploitation of this vulnerability aligns with techniques described in the ATT&CK framework under the T1059.007 sub-technique for "Command and Scripting Interpreter: JavaScript" as well as T1203 for "Exploitation for Client Execution." Attackers typically craft malicious web pages or email content that contains specially designed text elements that, when rendered by the vulnerable browser, trigger the out-of-bounds read condition. The memory access patterns involved in this vulnerability make it particularly attractive for information disclosure attacks that can be used to defeat modern security mitigations such as ASLR and stack canaries. Security researchers have noted that this type of vulnerability often serves as a stepping stone in more complex attack chains where the initial memory disclosure is used to leak addresses of system libraries or other security mechanisms, enabling subsequent exploitation techniques.
Mitigation strategies for this vulnerability primarily involve immediate software updates and patches provided by Mozilla to address the specific bounds checking issues in the text layout processing code. Organizations should prioritize patching all affected versions of Firefox, Thunderbird, and Firefox ESR to prevent exploitation. Additionally, implementing content security policies and restricting the execution of untrusted JavaScript can help reduce the attack surface. Network-level protections such as web application firewalls and intrusion detection systems can be configured to detect and block malicious content patterns associated with this vulnerability. The fix typically involves adding proper bounds checking mechanisms to ensure that glyph width calculations remain within allocated memory boundaries, preventing any potential out-of-bounds memory access during text rendering operations. Security monitoring should include detection of unusual memory access patterns and application crashes that may indicate exploitation attempts.