CVE-2015-7219 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 malformed PushPromise frame that triggers decompressed-buffer length miscalculation and incorrect memory allocation.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability identified as CVE-2015-7219 represents a critical flaw in the HTTP/2 protocol implementation within Mozilla Firefox browsers prior to version 43.0. This issue manifests as an integer underflow condition that occurs during the processing of malformed PushPromise frames, which are part of the HTTP/2 standard designed to improve web performance by allowing servers to proactively send resources to clients. The flaw exists within the decompression logic of Firefox's HTTP/2 parser, where incorrect buffer length calculations lead to improper memory allocation patterns that can result in application instability.
The technical exploitation of this vulnerability involves crafting malicious PushPromise frames that contain malformed data structures, specifically targeting the decompression buffer sizing calculations. When Firefox attempts to process these frames, the integer underflow causes the system to allocate insufficient memory for decompressed content, leading to assertion failures and ultimately causing the browser application to terminate unexpectedly. This type of vulnerability falls under the CWE-190 category of Integer Overflow or Wraparound, specifically manifesting as an integer underflow condition that bypasses normal memory allocation safeguards. The flaw demonstrates how protocol implementation errors can create exploitable conditions that allow remote attackers to disrupt service availability without requiring authentication or privileged access.
From an operational perspective, this vulnerability presents a significant risk to users who may encounter malicious websites or web content that triggers the flawed HTTP/2 processing path. The denial of service impact extends beyond simple browser crashes to potentially disrupt user productivity and create opportunities for more sophisticated attacks that leverage the application instability. Attackers can craft specific HTTP/2 responses containing the malformed PushPromise frames, which when processed by vulnerable Firefox versions, will cause immediate application termination. The vulnerability aligns with ATT&CK technique T1499.004 for Network Denial of Service, as it enables remote attackers to disrupt service availability through protocol manipulation. This type of attack vector is particularly concerning in enterprise environments where users may encounter untrusted web content or where attackers could leverage this flaw in phishing campaigns or web-based attack scenarios.
The mitigation strategy for CVE-2015-7219 centers on upgrading to Firefox version 43.0 or later, which includes fixes for the integer underflow condition in HTTP/2 frame processing. Organizations should also implement network-level controls such as web application firewalls that can detect and block malformed HTTP/2 frames, though this approach may not be comprehensive given the complexity of protocol-level vulnerabilities. Security teams should monitor for indicators of compromise related to HTTP/2 traffic patterns that might suggest exploitation attempts, particularly in environments where users may be exposed to untrusted web content. Additionally, browser hardening measures such as disabling HTTP/2 support in environments where it is not required can serve as a temporary workaround while ensuring full patch deployment occurs across all affected systems. The vulnerability underscores the importance of thorough protocol implementation testing and the need for robust input validation in network protocol handlers to prevent similar issues from occurring in other software components.