CVE-2026-56582: HCL MyCloud Information Disclosure Flaw

CVE-2026-56582 Overview

CVE-2026-56582 affects HCL MyCloud version 10.8.1 and exposes the product to the SSL/TLS LUCKY13 vulnerability. LUCKY13 is a padding oracle attack that targets the CBC-mode cipher suites used in TLS and DTLS implementations. An attacker positioned on the network can measure timing differences in MAC verification failures to recover small portions of plaintext from encrypted sessions. The flaw is categorized under [CWE-327] (Use of a Broken or Risky Cryptographic Algorithm). Exploitation requires network adjacency, low privileges, and a high attack complexity, which limits real-world impact but does not eliminate it for long-lived sessions carrying sensitive data.

Critical Impact
Attackers on the network path can perform a padding oracle attack against CBC-mode TLS sessions in HCL MyCloud 10.8.1 to recover fragments of sensitive plaintext.

Affected Products

HCL MyCloud 10.8.1
Deployments using CBC-mode TLS/SSL cipher suites
Any MyCloud endpoint terminating vulnerable TLS negotiations

Discovery Timeline

2026-07-21 - CVE-2026-56582 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-56582

Vulnerability Analysis

The LUCKY13 attack exploits a timing side channel in the MAC-then-encrypt construction used by TLS CBC cipher suites. When a TLS record is decrypted, the implementation removes CBC padding and then verifies the HMAC. Because valid padding and invalid padding cause slightly different amounts of HMAC computation, an attacker who observes precise timing of the server's error response can distinguish between the two cases. Repeating this observation across many crafted ciphertexts allows recovery of plaintext bytes one at a time. HCL MyCloud 10.8.1 exposes this behavior because it continues to negotiate CBC-mode cipher suites without adequate constant-time countermeasures.

Root Cause

The root cause is the continued use of a risky cryptographic construction, specifically CBC-mode ciphers combined with HMAC in TLS 1.0/1.1 and older TLS 1.2 configurations. The MAC-then-encrypt design and non-constant-time padding removal create the observable side channel that LUCKY13 abuses.

Attack Vector

Exploitation requires an attacker with a network position that can observe or interact with encrypted MyCloud sessions. The attacker sends large numbers of crafted TLS records and measures the server's response timing to infer padding validity. Successful exploitation is slow, statistical, and constrained to recovering short, predictable plaintext segments such as authentication cookies or session tokens transmitted repeatedly in the same position within TLS records.

No public proof-of-concept code is listed for this specific advisory. The vulnerability mechanism follows the well-documented LUCKY13 research against TLS CBC cipher suites, and no MyCloud-specific exploit is publicly available.

Detection Methods for CVE-2026-56582

Indicators of Compromise

Sustained, high-volume TLS handshakes or record traffic from a single source targeting a MyCloud endpoint.
Unusually high counts of TLS alert messages such as bad_record_mac originating from MyCloud servers.
Long-lived TLS sessions repeatedly negotiating CBC cipher suites when modern clients would prefer AEAD.

Detection Strategies

Inventory TLS configurations on MyCloud hosts and flag any endpoint still offering CBC-mode cipher suites.
Enable TLS handshake logging and alert on repeated negotiation of TLS_RSA_WITH_AES_*_CBC_* or similar CBC suites.
Correlate network telemetry to identify clients generating disproportionate volumes of TLS records against MyCloud services.

Monitoring Recommendations

Monitor HCL MyCloud web tier logs for repeated MAC verification failures over short intervals.
Track outbound alerts and cipher suite selection metrics from load balancers terminating TLS in front of MyCloud.
Baseline normal TLS session lengths and alert on statistical anomalies that could indicate a padding oracle probe.

How to Mitigate CVE-2026-56582

Immediate Actions Required

Review the HCL Software Knowledge Base Article KB0132381 and apply the vendor guidance for HCL MyCloud 10.8.1.
Disable all CBC-mode cipher suites on MyCloud endpoints and prefer AEAD suites such as AES-GCM or ChaCha20-Poly1305.
Restrict TLS negotiation to TLS 1.2 with AEAD ciphers or TLS 1.3.

Patch Information

Refer to the HCL Software Knowledge Base Article for the authoritative remediation guidance and any product updates from HCL for MyCloud.

Workarounds

Terminate TLS at a hardened reverse proxy or load balancer that enforces AEAD-only cipher suites in front of MyCloud.
Remove TLS 1.0 and TLS 1.1 support entirely from MyCloud-facing services.
Rotate any long-lived session tokens or credentials that may have traversed vulnerable CBC sessions.

bash

# Configuration example: restrict cipher suites to AEAD only (nginx)
ssl_protocols TLSv1.2 TLSv1.3;
ssl_ciphers 'TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305';
ssl_prefer_server_ciphers on;