CVE-2015-7218 in Firefox
Summary
by MITRE
The HTTP/2 implementation in Mozilla Firefox before 43.0 allows remote attackers to cause a denial of service (integer underflow, assertion failure, and application exit) via a single-byte header frame that triggers incorrect memory allocation.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/01/2022
The vulnerability identified as CVE-2015-7218 represents a critical flaw in Mozilla Firefox's HTTP/2 protocol implementation that could be exploited to achieve remote denial of service conditions. This issue affects Firefox versions prior to 43.0 and stems from improper handling of header frame processing within the HTTP/2 communication stack. The vulnerability specifically manifests when the browser receives a single-byte header frame that triggers incorrect memory allocation behavior, leading to system instability and potential application termination.
The technical root cause of this vulnerability lies in an integer underflow condition that occurs during the processing of HTTP/2 header frames. When Firefox encounters a malformed single-byte header frame, the implementation fails to properly validate the frame size parameters, resulting in a mathematical underflow that causes memory allocation calculations to produce invalid values. This flaw maps directly to CWE-191, which describes integer underflow conditions that can lead to memory corruption and system instability. The assertion failure that follows the underflow condition represents the system's built-in safety mechanism detecting the invalid state, ultimately causing the application to exit abruptly rather than gracefully handling the malformed input.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides attackers with a reliable method to crash Firefox instances remotely without requiring any special privileges or user interaction. The single-byte nature of the malicious frame makes this attack vector particularly efficient and difficult to detect in network traffic analysis. Attackers can craft specifically formatted HTTP/2 responses that trigger the integer underflow condition, causing Firefox to consume excessive resources or enter an unstable state that results in complete application termination. This behavior aligns with ATT&CK technique T1499.004, which describes denial of service attacks that target application stability through resource exhaustion or memory corruption.
The memory allocation failure that occurs as a result of this vulnerability demonstrates the broader class of issues that can arise when network protocol implementations fail to properly validate input data. HTTP/2's complex frame structure and header compression mechanisms create numerous potential attack surfaces where malformed data can cause unexpected behavior in client implementations. This vulnerability highlights the importance of rigorous input validation and boundary checking in protocol implementations, particularly for high-level network protocols that handle complex binary data structures. The fact that this issue affects the core HTTP/2 implementation means that all Firefox users who have HTTP/2 enabled are potentially at risk, regardless of the specific web content they are accessing. Organizations should prioritize updating their Firefox installations to version 43.0 or later to mitigate this vulnerability, as the fix addresses the underlying integer underflow condition and implements proper validation of header frame parameters to prevent similar issues in future implementations.