openssl_encrypt CVE-2026-81718

Exploitation requires the attacker to first obtain a keyfile or encrypted file produced by openssl_encrypt - through exfiltration, backup compromise, cloud storage misconfiguration, or physical access. Once the protected material is in hand, the remainder of the attack is entirely offline and requires no authentication or network access to the target system. The most critical condition applies to the dual-encryption file-password path, which uses only 10,000 PBKDF2-HMAC-SHA256 iterations - trivially defeated by GPU-accelerated brute-force against any non-random password. The PQC keyfile path (100,000 iterations) requires more compute but remains feasible for resourced adversaries. The vulnerability does not affect deployments that use neither PQC keyfile encryption nor the dual-encryption file-password feature. The principal limiting factor for real-world risk is the access controls protecting storage of keyfiles and encrypted files; strong storage isolation materially reduces but does not eliminate risk, since the underlying cryptographic weakness persists in all previously generated protected material.

The CVSS 4.0 score of 8.7 with AV:N/AC:L/AT:N/PR:N/UI:N reflects the high confidentiality impact upon successful exploitation, but overstates ease of attack by treating material acquisition as a non-factor. The attack is entirely offline once keyfiles or encrypted files are obtained - no continued network access to the target system is required. EPSS data was not provided in the available intelligence, limiting probabilistic exploitation forecasting. The vulnerability is not listed in CISA KEV and no public exploit code has been identified, indicating no confirmed active exploitation at time of analysis. However, the technical barrier to exploit is extremely low for any adversary with GPU resources: 10,000 PBKDF2 iterations can be exhausted against common password spaces in minutes, and even a mid-sized organization running this library for PQC-protected data should treat upgrading as urgent given that any previously exfiltrated material is retroactively at risk. The real-world priority is therefore governed primarily by storage exposure of keyfiles and encrypted files, not by network perimeter controls.

An attacker who compromises a backup server, cloud storage bucket, or shared network filesystem containing openssl_encrypt keyfiles copies the protected material offline. Using a GPU cluster running a PBKDF2-HMAC-SHA256 cracking tool such as Hashcat, the attacker exhausts the 10,000-iteration file-password verification hash against a common password dictionary in minutes, then uses the recovered password to decrypt the associated private key or plaintext without requiring any further access to the victim system. No public exploit code has been identified at time of analysis, but standard GPU cracking tooling requires minimal adaptation for this attack.