CVE-2016-7127 in PHP
Summary
by MITRE
The imagegammacorrect function in ext/gd/gd.c in PHP before 5.6.25 and 7.x before 7.0.10 does not properly validate gamma values, which allows remote attackers to cause a denial of service (out-of-bounds write) or possibly have unspecified other impact by providing different signs for the second and third arguments.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-7127 resides within the PHP GD extension's imagegammacorrect function, which is part of the broader graphics manipulation capabilities available in PHP applications. This flaw affects PHP versions prior to 5.6.25 and 7.x versions prior to 7.0.10, representing a critical security issue that could be exploited by remote attackers to compromise system availability and potentially execute arbitrary code. The vulnerability stems from inadequate input validation mechanisms within the gamma correction functionality that processes image data, specifically when handling gamma values during image processing operations.
The technical flaw manifests through improper validation of gamma parameters within the imagegammacorrect function implementation in ext/gd/gd.c. When attackers provide gamma values with differing signs for the second and third arguments, the function fails to properly sanitize these inputs before processing them in memory operations. This oversight creates an out-of-bounds write condition that can be leveraged to overwrite adjacent memory locations, potentially leading to denial of service scenarios where application processes crash or become unresponsive. The vulnerability operates under CWE-129, which classifies it as an Improper Validation of Array Index, while also relating to CWE-787, the out-of-bounds write condition that can result from insufficient input validation. The flaw represents a classic buffer over-read/write vulnerability that occurs when the application does not adequately verify the range and sign of numeric parameters before using them in memory operations.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attack vectors that could compromise system integrity. Remote attackers can exploit this weakness by crafting malicious image files or manipulating image processing parameters in web applications that utilize the affected PHP versions. When exploited, the vulnerability can cause application crashes, leading to service disruption and potential information disclosure through memory corruption. The attack surface is particularly broad since many web applications process user-uploaded images through PHP's GD library, making this vulnerability applicable to numerous web platforms including content management systems, file upload handlers, and image processing services. This vulnerability aligns with ATT&CK technique T1203, which involves exploiting weaknesses in input validation to achieve system compromise.
Mitigation strategies for CVE-2016-7127 primarily involve immediate patching of affected PHP installations to versions 5.6.25 or 7.0.10 and later, which contain the necessary input validation fixes. Organizations should implement comprehensive vulnerability management processes that include regular security updates and patch deployment cycles to prevent exploitation of similar flaws. Additional defensive measures include input validation at multiple layers of application architecture, implementing strict parameter validation for image processing functions, and monitoring for anomalous image processing activities. Network segmentation and application firewalls can provide additional protection by limiting access to vulnerable image processing endpoints. Security teams should also consider implementing automated scanning tools that can detect vulnerable PHP versions and monitor for exploitation attempts targeting this specific vulnerability. The fix implemented in patched versions ensures proper validation of gamma parameter signs and ranges, preventing the out-of-bounds memory operations that previously enabled exploitation.