A security flaw in Mu PDF and other PDF editors allows attackers to crack AES-256 encryption by exploiting weak random number generation. Researchers discovered that Mu PDF uses only 9 bits of entropy from a timestamp to generate its 32-byte file key, drastically reducing the keyspace to 512 possible keys. Other editors like Foxit face similar issues by relying on time-based randomness.
This vulnerability enables passwordless decryption of protected documents in milliseconds. The flaw stems from using a linear congruential generator seeded with the current epoch, where only a fraction of the state bits influence the output. By brute-forcing all 512 combinations, attackers can recover the key and bypass encryption entirely, rendering PDF security ineffective against even basic attacks.
Source: Hacker News · Summarized by HeadlinesBriefing