本文详细分析了libFontParser.dylib库中存在的CFF2字体解析漏洞，该漏洞源于混合操作码(blend opcode)参数验证不足导致的堆栈越界访问，攻击者可通过特制字体文件实现代码执行，影响macOS/iOS系统安全。
根本原因
半年前在CoreGraphics库的libFontParser.dylib组件中发现漏洞，该组件负责macOS/iOS/iPadOS系统的字体解析渲染。漏洞存在于TType1FontType2CharStringHandler::InterpreteCharString函数处理CFF2字符集的混合操作码(blend opcode)时。
关键问题点：
n_blend是栈顶弹出的最后一个值k是攻击者可控的数值nargs_left = nargs - 1（不包括已弹出的n_blend）
根据OTF-CFF2规范，混合参数应通过公式计算：
n_blend * k + n_blend
但实际汇编代码显示仅检查了v2 = n_blend * k，随后通过buffer = (signed __int64)&stack[-v103]获取栈缓冲区指针时产生越界访问。
漏洞验证
构造包含以下恶意操作码的OTF字体：
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