CVE-2019-3557 in HHVM
Summary
by MITRE
The implementations of streams for bz2 and php://output improperly implemented their readImpl functions, returning -1 consistently. This behavior caused some stream functions, such as stream_get_line, to trigger an out-of-bounds read when operating on such malformed streams. The implementations were updated to return valid values consistently. This affects all supported versions of HHVM (3.30 and 3.27.4 and below).
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Analysis
by VulDB Data Team • 07/01/2023
The vulnerability identified as CVE-2019-3557 represents a critical implementation flaw within the HyperText Hack Virtual Machine HHVM runtime environment, specifically affecting stream handling mechanisms for bz2 and php://output streams. This issue stems from improper function implementations where the readImpl methods consistently return -1 values, creating a fundamental inconsistency in stream operation behavior that extends beyond simple data retrieval failures. The flaw manifests in how HHVM processes stream operations, particularly when stream_get_line and similar functions attempt to process these malformed streams, leading to unpredictable system behavior and potential security implications.
The technical root cause of this vulnerability lies in the inconsistent return value handling within the stream abstraction layer of HHVM's implementation. When stream functions encounter streams that improperly implement their readImpl methods by consistently returning -1, the underlying stream processing logic becomes vulnerable to out-of-bounds read conditions. This occurs because the stream processing algorithms expect valid return codes that indicate proper data consumption or end-of-stream conditions, but instead receive negative values that trigger unexpected code paths within the stream handling subsystem. The improper implementation creates a scenario where legitimate stream operations can inadvertently access memory locations beyond the intended data boundaries, potentially exposing sensitive information or causing system instability.
From an operational impact perspective, this vulnerability affects all supported versions of HHVM including versions 3.30 and 3.27.4 and below, creating widespread exposure across numerous production environments that rely on HHVM for web application execution. The out-of-bounds read conditions can lead to information disclosure, application crashes, or potentially more severe consequences if exploited in conjunction with other vulnerabilities within the same runtime environment. Security analysts should note that this issue aligns with CWE-129, which addresses improper validation of array indices and other bounds checking failures, and may potentially map to ATT&CK technique T1059.007 for command and scripting interpreter execution in contexts where stream manipulation could be leveraged for privilege escalation or data exfiltration.
The remediation approach for this vulnerability requires immediate patching of affected HHVM installations to ensure that the stream implementations properly return valid values consistent with expected stream operation behaviors. Organizations should prioritize updating their HHVM deployments to versions that contain the corrected readImpl function implementations, as the fix addresses the core issue by ensuring that stream operations return appropriate status codes that align with standard stream handling conventions. System administrators should also conduct thorough testing of applications that utilize bz2 and php://output streams to verify that the updated implementations do not introduce regressions in existing functionality while ensuring that the out-of-bounds read conditions have been properly resolved.