安全研究人员发现，MuPDF、Foxit、OpenPDF和iText等多个主流PDF实现存在严重加密漏洞 1。尽管这些软件宣称使用AES-256标准进行加密，但由于密钥生成机制依赖于极小的状态空间或不安全的随机源（如时间戳），攻击者无需获取密码即可通过暴力破解手段解密文档 1。其中，MuPDF在1.28.5版本之前利用drand48函数生成随机数，导致仅有9位来自时间戳的状态真正影响AES-256密钥，使得实际密钥空间缩减至仅512种可能 1。Foxit PDF Reader（版本2026.1.3.36551）则基于当前时间戳哈希生成密钥，且存在未初始化字节为零的问题，允许攻击者通过多线程技术在毫秒级时间内恢复密钥 1。
这一有缺陷的密钥推导模式可追溯至2014年5月PDFium的首次公开提交，其原始代码归属于Foxit 1。此外，OpenPDF 3.0.5和iText 9.7.1也受到影响，它们通过ARC4流生成随机数，种子来源为毫秒时间戳和JVM空闲内存，同样易受攻击 1。研究团队已发布针对MuPDF和Foxit的专用解密工具以验证漏洞 1。目前MuPDF的相关漏洞已完成修复，但此前生成的加密文档仍面临安全风险；而Foxit等其他厂商的代码问题源于早期开源库或继承代码，导致旧文档无法进行追溯性保护 1。
Security researchers have uncovered critical cryptographic vulnerabilities in several mainstream PDF processing libraries, including MuPDF, Foxit, OpenPDF, and iText. 1 Although these applications advertise the use of AES-256 encryption, the actual security is compromised because file keys are derived from extremely small state spaces or insecure random sources, such as timestamps. 1 This flaw allows attackers to brute-force and decrypt documents without needing the user's password. 1
The investigation revealed specific implementation errors across different software versions. In MuPDF versions prior to 1.28.5, the drand48 function was used for randomness, meaning only 9 bits of state derived from timestamps influenced the AES-256 key, resulting in a negligible keyspace of just 512 possibilities. 1 Similarly, Foxit PDF Reader version 2026.1.3.36551 generated keys based on a hash of the current timestamp, with uninitialized bytes set to zero, enabling multi-threaded brute-force searches to recover the key in milliseconds. 1 Researchers traced this defective key derivation pattern back to the first public commit of PDFium in May 2014, noting that the original code belonged to Foxit. 1
Other affected libraries exhibit comparable weaknesses due to poor seeding practices. OpenPDF 3.0.5 and iText 9.7.1 generate random numbers using an ARC4 stream seeded by millisecond timestamps and JVM idle memory, making them equally susceptible to attack. 1 While the research team has released decryption tools targeting MuPDF and Foxit, and the vulnerability in MuPDF has been patched, documents encrypted with these flawed implementations remain at risk. 1 Issues stemming from early open-source libraries or inherited code in other vendors, such as Foxit, cannot be retroactively fixed for previously created files. 1
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