CVE-2026-56582

Executive Summary

Business Impact: HCL MyCloud, a cloud-based file sharing and collaboration platform, is affected by a cryptographic weakness in its TLS/SSL implementation. This vulnerability exposes encrypted data in transit to a theoretical decryption risk. The likely attacker is a sophisticated threat actor capable of man-in-the-middle (MITM) attacks, potentially targeting enterprise users who rely on MyCloud for sensitive document exchange. Industries such as finance, legal, and healthcare, which use MyCloud for secure file sharing, are at the highest risk.

Vulnerability Class & Attack Vector: This is a padding oracle attack against TLS/SSL, specifically the "LUCKY13" vulnerability (CWE-310: Cryptographic Issues). The attack vector is network-based, requiring the attacker to be positioned on the network path between the client and the HCL MyCloud server. The attack does not require authentication but does require the ability to intercept and modify network traffic.

Urgency Assessment: The CVSS 3.1 base score is 3.1 (Low). The EPSS exploitation probability is 0.0%, indicating a very low likelihood of exploitation in the wild in the near term. While the technical impact (confidentiality breach) is significant, the high complexity of the attack and the lack of a known exploit or patch significantly reduce the immediate urgency. This is a vulnerability to monitor and plan for, rather than one requiring an emergency response.

Key Facts:

• Vendor: HCL
• Affected Software: HCL MyCloud
• Patch Status: Unpatched / Unknown
• CISA KEV: Not listed.

CVSS Breakdown & Threat Level

Qualitative Severity: Low

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Metric Decomposition:

• AV:N (Network): The attack is launched over the network. The attacker does not need physical or local access to the target system.
• AC:H (High): Exploitation requires a man-in-the-middle position, precise timing, and the ability to perform a large number of TLS handshakes to decrypt a small amount of data. This is not a simple, single-packet exploit.
• PR:N (None): The attacker does not need any prior authentication or access to the HCL MyCloud system.
• UI:N (None): The victim does not need to perform any action beyond normal use of the MyCloud service. The attack is transparent to the user.
• S:U (Unchanged): A successful attack compromises the confidentiality of the TLS session but does not allow the attacker to compromise other components of the system.
• C:L (Low): The attack can only decrypt a limited amount of data (e.g., session cookies or small pieces of plaintext) per successful attempt. There is no total loss of confidentiality.
• I:N (None): The attack does not allow the attacker to modify any data.
• A:N (None): The attack does not affect the availability of the service.

EPSS Interpretation: An EPSS score of 0.0% means that as of the publication date, the model predicts a near-zero probability of exploitation in the wild within the next 30 days. This is consistent with the high attack complexity and the lack of a public exploit.

Historical Comparison: This vulnerability is similar to CVE-2013-0169 (Lucky13) which affected OpenSSL and other TLS implementations. Like CVE-2013-0169, this is a timing side-channel attack on CBC-mode ciphers in TLS. The low CVSS score reflects the difficulty of exploitation compared to other TLS vulnerabilities like Heartbleed (CVE-2014-0160), which allowed direct memory reading.

Temporal & Environmental Considerations: With no patch available and no exploit code, the temporal score remains low. Organizations that use HCL MyCloud in highly sensitive environments (e.g., handling classified data) should consider this a higher risk due to the potential for data leakage, even if the probability is low.

Technical Deep Dive & Attack Mechanics

Step-by-Step Technical Explanation:

The LUCKY13 attack exploits a timing side-channel in the TLS protocol's handling of CBC-mode cipher suites (e.g., TLS_RSA_WITH_AES_128_CBC_SHA). The attack works as follows:

1. Man-in-the-Middle (MITM) Position: The attacker must be able to intercept and modify network traffic between the HCL MyCloud client and server.
2. Session Interception: The attacker captures a TLS session and records the encrypted ciphertext.
3. Padding Oracle: The attacker modifies the ciphertext and sends it to the server. The server's response time (or error message) reveals whether the padding of the decrypted block is valid. This is the "padding oracle."
4. Timing Analysis: The key to LUCKY13 is that the time it takes for the server to process a CBC record depends on the number of padding bytes. By measuring these timing differences (on the order of microseconds), the attacker can determine if their guess for a plaintext byte is correct.
5. Byte-by-Byte Decryption: The attacker uses this oracle to decrypt the ciphertext one byte at a time, typically targeting sensitive data like session cookies.

Root Cause Analysis: The root cause is a combination of the TLS protocol specification and the implementation in HCL MyCloud. The TLS 1.0/1.1 specification for CBC-mode encryption does not mandate constant-time processing of padding. The HCL MyCloud implementation likely processes valid and invalid padding with slightly different code paths, leading to measurable timing differences.

Attack Surface:

• Ports/Protocols: TCP port 443 (HTTPS) using TLS 1.0, 1.1, or 1.2 with CBC-mode cipher suites.
• Interface: The public-facing web interface of HCL MyCloud.

Pre-conditions:

• Network access to perform a MITM attack (e.g., on the same local network, compromised router, or malicious Wi-Fi hotspot).
• The TLS session must use a CBC-mode cipher suite (e.g., AES-CBC, 3DES-CBC).
• The attacker must be able to send a large number of modified TLS records (typically millions) to decrypt a single block of data.

Attack Variants:

• LUCKY13 (Original): Targets the TLS record processing time.
• LUCKY13 Micro: A more refined variant that uses even more precise timing measurements.

Why Standard Defenses May Fail:

• Firewalls: Cannot detect the attack as it uses standard TLS traffic.
• IDS/IPS: The attack traffic looks like normal TLS handshakes and encrypted data. Timing differences are not visible at the network level.
• WAF: Cannot inspect encrypted TLS payloads.

Vulnerable vs. Patched Code Analysis

Note: As no patch or specific code details are available from the provided data, this section is based on the general nature of the LUCKY13 vulnerability.

Vulnerable Code (Pseudocode):

// Vulnerable implementation: non-constant time padding check
int tls_decrypt_cbc(unsigned char *record, int len) {
    // ... decryption logic ...
    int padding_len = record[len-1];
    // Check padding (non-constant time)
    for (int i = 0; i <= padding_len; i++) {
        if (record[len-1-i] != padding_len) {
            // Early exit on invalid padding (timing leak)
            return TLS_DECRYPT_FAIL;
        }
    }
    // ... process plaintext ...
}

Patched Code (Pseudocode):

// Patched implementation: constant-time padding check
int tls_decrypt_cbc(unsigned char *record, int len) {
    // ... decryption logic ...
    int padding_len = record[len-1];
    int check = 0;
    // Check all padding bytes in constant time
    for (int i = 0; i <= padding_len; i++) {
        check |= (record[len-1-i] ^ padding_len);
    }
    if (check != 0) {
        return TLS_DECRYPT_FAIL;
    }
    // ... process plaintext ...
}

What the Patch Changes: The patch replaces the early-exit loop with a loop that processes all bytes and accumulates the result. This ensures that the time taken to validate the padding is independent of the padding value, eliminating the timing side-channel.

Regression Considerations: The primary risk is performance. Constant-time operations can be slightly slower. However, the security benefit far outweighs the negligible performance impact.

Timeline & Disclosure History

• CVE Publication Date: 2026-07-21T18:17:02.170
• Estimated Discovery Timeline: Unknown. The vulnerability was likely discovered through internal security research or responsible disclosure.
• Disclosure Process: The CVE was assigned by the CNA (likely HCL or a third-party coordinator). The details were made public on the NVD on the publication date.
• Known Exploitation in the Wild: No known active exploitation as of 2026-07-21.
• CISA KEV Addition Date: Not applicable.

Threat Intelligence Context

Threat Actor Profile: This vulnerability is most likely to be exploited by nation-state actors or advanced persistent threat (APT) groups with significant resources. The attack requires a MITM position and the ability to perform complex timing analysis. Script kiddies and ransomware operators are unlikely to have the capability or patience for this attack.

Attack Campaign Context: No specific campaigns are known to be associated with this CVE. It is a general cryptographic weakness that could be used in targeted espionage operations.

Geographic Targeting Patterns: Unknown. The attack is opportunistic, targeting any user of HCL MyCloud who is on a network the attacker controls.

Industry Verticals Most at Risk:

• Government & Defense: For secure document sharing.
• Financial Services: For sharing sensitive financial data.
• Legal: For sharing confidential client documents.
• Healthcare: For sharing protected health information (PHI).

Connection to Similar Vulnerabilities: This is a re-emergence of the classic LUCKY13 attack (CVE-2013-0169) in a specific product. It highlights the ongoing challenge of implementing TLS correctly.

Exploitation & Lab Setup

Red Team Section

Lab Setup:

1. Environment: Two virtual machines (VMs) on an isolated network.
   • Victim VM: Runs a vulnerable version of HCL MyCloud (if available) or a generic TLS server with CBC-mode ciphers enabled.
   • Attacker VM: Kali Linux with tools like tls-attacker or a custom Python script for the LUCKY13 attack.
2. Network Configuration: The attacker VM must be configured as a MITM (e.g., using ARP spoofing or a transparent proxy).
3. Prerequisites:
   • Vulnerable HCL MyCloud instance.
   • Python 3 and scapy or scapy-ssl_tls for crafting TLS records.

Exploitation Walkthrough:

1. Setup MITM: Use arpspoof to redirect traffic between the victim and the HCL MyCloud server through the attacker VM.
2. Capture Session: Use tcpdump to capture a TLS session between the victim and the server.
3. Run LUCKY13 Attack: Execute a LUCKY13 attack script that:
   • Intercepts the TLS session.
   • Modifies ciphertext blocks.
   • Sends them to the server.
   • Measures response times to determine plaintext bytes.
4. Expected Output: The attacker will successfully decrypt a small portion of the TLS session, such as a session cookie or a password.

Post-Exploitation: With a decrypted session cookie, the attacker can hijack the victim's session and access the HCL MyCloud application as that user.

Blue Team Section

Detection:

• Network: Monitor for an unusually high number of TLS connections from a single IP address to the HCL MyCloud server. Look for connections that are very short-lived (a few milliseconds) and involve many renegotiations.
• Endpoint: On the server, monitor for high CPU usage related to TLS decryption. Log entries showing repeated TLS decryption failures or errors may indicate an attack.
• Log Entries: Look for patterns of TLS decryption failed or bad_record_mac errors occurring in rapid succession from the same client IP.

Indicators of Compromise (IOCs)

No confirmed IOCs available — the following patterns are illustrative of exploitation attempts:

• Network IOCs:
  • High volume of TLS ClientHello messages from a single source IP to the target server (e.g., >1000 per minute).
  • TLS connections with a very short duration (< 1 second) and small data transfer.
  • Repeated TLS renegotiation attempts from the same client.
• HTTP Request Patterns: Not applicable, as the attack occurs at the TLS layer.
• File System Artifacts: None.
• Process Execution Anomalies: High CPU usage by the TLS/SSL process on the HCL MyCloud server.
• Log Entries:
  • [EXAMPLE — not a real log] TLS error: decryption failed from IP 10.0.0.5
  • [EXAMPLE — not a real log] SSL: SSL3_GET_RECORD:decryption failed or bad record mac

Detection Engineering

YARA Rule

rule CVE-2026-56582_LUCKY13_Traffic {
    meta:
        description = "Detects network traffic patterns associated with LUCKY13 attack on TLS CBC-mode ciphers"
        author = "Valters IT Hub"
        date = "2026-07-21"
        reference = "https://www.valtersit.com/cve/cve-2026-56582"
    strings:
        $tls_content_type_alert = { 15 }  // TLS Content Type: Alert (21 = 0x15)
        $tls_alert_desc_bad_record_mac = { 20 } // Alert Description: Bad Record MAC (20 = 0x14)
        $tls_cipher_suite_cbc = { 00 2F }  // TLS_RSA_WITH_AES_128_CBC_SHA (0x002F)
    condition:
        $tls_content_type_alert at 0 and $tls_alert_desc_bad_record_mac and $tls_cipher_suite_cbc
}

Sigma Rule (SIEM)

title: CVE-2026-56582 HCL MyCloud LUCKY13 Exploitation Attempt
id: f7dd9976-1338-4f68-8f0d-2f2e71e34d73
status: experimental
description: Detects a high volume of TLS errors from a single source IP, indicative of a LUCKY13 padding oracle attack.
author: Valters IT Hub
date: 2026-07-21
references:
    - https://www.valtersit.com/cve/cve-2026-56582
logsource:
    category: webserver
    product: hcl_mycloud
detection:
    selection:
        EventID: 36888  # Example: Windows Schannel event for TLS error
        SourceIp:
            - '10.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
    condition: selection | count() by SourceIp > 100 within 1m
falsepositives:
    - Legitimate clients with misconfigured TLS stacks.
    - Network scanning tools.
level: high

Suricata IDS Rule

alert tls $EXTERNAL_NET any -> $HOME_NET 443 (msg:"CVE-2026-56582 LUCKY13 Attack - High Volume of TLS Errors"; flow:to_server; tls.version:<=3.3; content:"|15 14|"; threshold: type both, track by_src, count 100, seconds 60; classtype:attempted-recon; sid:1000001; rev:1;)

Elastic (EQL) Query

// Detect high frequency of TLS errors from a single source IP
sequence by source.ip
  [network where network.protocol == "tls" and event.action == "error" and event.outcome == "failure"]
  with maxspan=1m
  | stats count by source.ip
  | where count > 100

Splunk SPL Query

index=windows EventCode=36888 SourceIp=* 
| stats count by SourceIp 
| where count > 100
| eval description="Potential LUCKY13 attack (CVE-2026-56582) from ".SourceIp

Wazuh Rule

<group name="hcl_mycloud,">
  <rule id="100001" level="12">
    <decoded_as>json</decoded_as>
    <field name="event_type">^tls_error$</field>
    <field name="src_ip" type="ip">.+</field>
    <description>CVE-2026-56582: Possible LUCKY13 attack from $(src_ip)</description>
    <options>no_full_log</options>
    <group>attack,tls,lucky13,</group>
  </rule>
</group>

Remediation & Mitigation

Immediate Actions (0-24 hours)

• Patch: No patch is available. Contact HCL support for an update.
• Compensating Controls:
  • Disable CBC-mode Cipher Suites: On the HCL MyCloud server, disable all CBC-mode cipher suites (e.g., TLS_RSA_WITH_AES_128_CBC_SHA, TLS_RSA_WITH_AES_256_CBC_SHA). Enable only AEAD ciphers like TLS_AES_128_GCM_SHA256 (TLS 1.3) or TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (TLS 1.2).
  • Enforce TLS 1.2 or 1.3: Disable TLS 1.0 and 1.1, which are more susceptible to this attack.
• Network-Level Mitigation: Implement network segmentation to reduce the risk of MITM attacks. Use VPNs for remote access.
• Authentication Hardening: Implement multi-factor authentication (MFA) to reduce the impact of session hijacking.

Short-term (1-7 days)

• Configuration Hardening: Review and harden the TLS configuration on the HCL MyCloud server.
• Monitoring Implementation: Deploy the detection rules provided in this report to monitor for exploitation attempts.
• Vulnerability Scanning: Use a TLS scanner (e.g., testssl.sh) to confirm that CBC-mode ciphers are disabled.
  • Command: testssl.sh --cipher-per-proto https://mycloud.example.com

Long-term

• Architecture Changes: Consider using a reverse proxy (e.g., Nginx, HAProxy) that terminates TLS with a secure configuration and forwards traffic to the backend.
• Security Control Improvements: Implement network traffic analysis tools that can detect timing-based attacks.
• Developer Training: Ensure developers are trained on secure TLS implementation and the importance of constant-time cryptography.

Validation: To confirm the fix, run a TLS scanner against the HCL MyCloud server and verify that no CBC-mode cipher suites are offered. Also, verify that TLS 1.0 and 1.1 are disabled.

References & Resources

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56582
• CVE.org: https://www.cve.org/CVERecord?id=CVE-2026-56582
• Vendor advisory: See vendor security page
• OSV: https://osv.dev/vulnerability/CVE-2026-56582 (if applicable)
• Related CWE: https://cwe.mitre.org/data/definitions/310.html
• MITRE ATT&CK: https://attack.mitre.org/techniques/T1190/

Report generated by Valters IT Hub Neural Engine v25 | 2026-07-21 | https://www.valtersit.com/cve/cve-2026-56582