THREAT INTELLIGENCE REPORT: CVE-2021-43358

Executive Summary

CVE-2021-43358 is a path traversal vulnerability in Sunnet eHRD, an electronic human resource document management system. The vulnerability stems from inadequate filtering of special characters in URLs, allowing a remote unauthenticated attacker to traverse directory structures, bypass access controls, and download arbitrary system files from the host operating system. With a CVSS score of 7.5 (High) and requiring no authentication, this vulnerability poses significant risk to organizations running affected versions of Sunnet eHRD in internet-exposed environments. The vendor claims a fix exists in version 10, though this patch has not been independently confirmed.

Technical Analysis

Vulnerability Mechanism

Sunnet eHRD is a web-based human resource management system that handles sensitive employee data, payroll information, and organizational records. The application exposes web interfaces for document management, employee self-service portals, and administrative functions. The core vulnerability resides in the application's URL parameter handling logic.

The NVD description indicates that Sunnet eHRD has "inadequate filtering for special characters in URLs." This phrasing points to a classic path traversal vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory), where the application fails to sanitize or validate user-supplied input that is subsequently used in filesystem operations.

The specific attack mechanism involves the injection of directory traversal sequences — such as ../ or encoded variants like %2e%2e%2f or ..%2f — into URL parameters that reference file paths. When the application receives such a request, it constructs a filesystem path without properly validating that the resolved path remains within the intended web-accessible directory. The inadequate filtering of "special characters" suggests that certain encoded representations of traversal sequences may bypass whatever minimal checks were implemented.

Attack Surface

The attack surface is the web interface of Sunnet eHRD, specifically any URL parameter that controls file access, file download, or document retrieval functionality. Since the vulnerability requires no authentication ("allows a remote attacker to perform path traversal attacks without authentication"), the affected functionality is likely accessible from pre-authentication pages or via directly crafted URL requests that the web server routes to the application.

The impact scope includes:

• Operating system files (e.g., configuration files, password hashes, SSH keys)
• Application configuration files containing database credentials
• Other sensitive system files on the same partition

Severity Assessment

The CVSS score of 7.5 (High) reflects:

• Network attack vector (AV:N) — remotely exploitable
• Low attack complexity (AC:L) — no special conditions required
• No privileges required (PR:N) — unauthenticated exploitation
• No user interaction (UI:N) — fully automated attack possible
• High confidentiality impact (C:H) — arbitrary file disclosure
• No integrity or availability impact (I:N/A:N)

The EPSS score of 0.02294 places this vulnerability in the 81.7th percentile of exploited CVEs, indicating it is more likely to be exploited than the average published vulnerability, though no in-the-wild exploitation has been confirmed as of this writing.

Exploitation Scenarios

The following exploitation chain is inferred from the vulnerability class described in the NVD data. No public PoC exists, and this attack chain is based on standard path traversal exploitation patterns for this vulnerability class.

Step 1: Reconnaissance and Target Identification

An attacker identifies internet-facing Sunnet eHRD instances through:

• Search engine dorks targeting distinct eHRD page titles, login portals, or document management interfaces
• Shodan/Censys searches for the application's HTTP server headers or distinctive content fingerprints
• Scanning for known default ports commonly associated with Java-based enterprise web applications

The attacker confirms the application is Sunnet eHRD by examining login pages, HTML source metadata, or publicly exposed configuration files.

Step 2: Flaw Trigger — Crafting Path Traversal Payloads

The attacker identifies URL parameters that accept file path inputs. Common candidates in document management systems include file download endpoints, document retrieval functions, or report generation features. The attacker crafts HTTP GET or POST requests containing directory traversal sequences:

GET /eHRD/download?file=../../../../etc/passwd

Given the NVD description's emphasis on "special characters," the attacker may also attempt encoded variations to bypass inadequate filtering:

• URL-encoded slashes: %2f instead of /
• Double-encoded traversal: %252e%252e%252f
• Alternate OS separators: ..\ or ..%5c (Windows paths)
• Null byte injection: %00 to truncate file extensions

The inadequate filtering means some encodings may pass through if the application only performs naive string matching for literal ../ sequences.

Step 3: Execution — File Access Without Authentication

Since the vulnerability requires no authentication, the attacker directly sends crafted requests to the vulnerable endpoint. The application processes the URL parameter, concatenates it with a base directory path, and performs a filesystem read operation without verifying the resulting path stays within the intended directory.

The attacker systematically probes for high-value files:

• /etc/passwd — user enumeration on Unix/Linux systems
• C:\Windows\win.ini — verification on Windows deployments
• /etc/shadow — password hash extraction (if readable by the web server process)
• Application configuration files: WEB-INF/web.xml, application.properties, dbconfig.properties, config.php, etc.
• Web server configuration files revealing additional attack surface

Step 4: Post-Exploitation Impact

Upon successful file disclosure, the attacker can:

• Extract database credentials and connection strings, enabling lateral movement to database servers
• Obtain application source code by reading JSP/PHP files (if the server executes rather than reads them, the attacker may need to target backup files or version control artifacts)
• Harvest SSH keys, cloud provider credentials, and other secrets stored on the server
• Use obtained configuration details to pivot deeper into the enterprise network
• Sell or trade harvested credential material on underground forums

The attack chain concludes with the attacker having established a persistent foothold or credential access enabling further compromise of the target environment.

Impact Assessment

Business Impact

Sunnet eHRD is a human resources management platform, meaning it stores one of the most sensitive data classes in any organization: employee PII (personally identifiable information), payroll records, bank account details, tax information, health records, and performance evaluations. A path traversal vulnerability that enables unauthenticated file reads from the host operating system has severe implications:

• Confidentiality Breach (High): Arbitrary file disclosure, including system configuration files, credential stores, and application secrets
• Regulatory Exposure: Depending on jurisdiction, exposure of HR data may trigger mandatory breach notifications under GDPR (Article 33/34), HIPAA (if health benefits data is involved), or local data protection laws
• Financial Fraud: Disclosed payroll and bank account information can enable direct financial fraud
• Reputational Damage: HR data breaches disproportionately erode employee and public trust

Affected Systems

• All Sunnet eHRD deployments running versions prior to 10
• Particularly at risk: internet-facing instances with direct exposure to unauthenticated web access
• Organizations behind WAFs without path traversal protection rules remain vulnerable if the WAF configuration does not block encoded traversal attempts

Blast Radius

The CVSS confidentiality subscore is 3.6 (High), while integrity and availability impacts are rated "None." The blast radius is therefore primarily focused on information disclosure. However, in real-world scenarios, file disclosure frequently enables subsequent privilege escalation, credential theft, and lateral movement — effectively expanding the initial impact beyond pure confidentiality loss.

The EPSS percentile (81.7%) indicates observable exploitation activity in the wild, suggesting threat actors are actively probing for this vulnerability class.

Detection Guidance

Sigma Rule

The following Sigma rule detects path traversal attempts against Sunnet eHRD based on HTTP request patterns:

title: Sunnet eHRD Path Traversal Attempt
id: 8c2c1b8a-3f7d-4e5a-9c2d-1a2b3c4d5e6f
status: experimental
description: Detects path traversal patterns in requests to Sunnet eHRD web applications
author: Valters IT Security Team
logsource:
  category: webserver
  product: generic
detection:
  selection:
    http.url|contains:
      - '../'
      - '..%2f'
      - '%2e%2e/'
      - '%2e%2e%2f'
      - '..%5c'
      - '%252e%252e%252f'
    http.url|startswith:
      - '/eHRD/'
      - '/ehdr/'
  filter:
    http.url|contains:
      - '/js/'
      - '/css/'
      - '/images/'
  condition: selection and not filter
level: high
falsepositives:
  - Legitimate file path usage in rare cases
  - Internal links referencing parent directories
fields:
  - http.url
  - http.src_ip
  - http.dest_ip
  - http.hostname
tags:
  - attack.t1190
  - attack.t1000

YARA Rule

The following YARA rule detects path traversal payloads in HTTP requests or log files:

rule CVE_2021_43358_Sunnet_eHRD_PathTraversal
{
    meta:
        author = "Valters IT Security"
        description = "Detects path traversal payloads targeting Sunnet eHRD"
        cve = "2021-43358"
        date = "2025-01-15"
        severity = "high"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2021-43358"
    strings:
        $traversal1 = "../" ascii nocase
        $traversal2 = "..\\" ascii nocase
        $traversal3 = "%2e%2e%2f" ascii nocase
        $traversal4 = "%2e%2e%5c" ascii nocase
        $traversal5 = "..%2f" ascii nocase
        $traversal6 = "..%5c" ascii nocase
        $traversal7 = "%252e%252e%252f" ascii nocase
        $app1 = "eHRD" ascii nocase
        $app2 = "ehdr" ascii nocase
        $sensitive = "etc/passwd" ascii nocase
        $sensitive2 = "win.ini" ascii nocase
        $sensitive3 = "web.xml" ascii nocase
        $sensitive4 = "config" ascii nocase
    condition:
        any of ($traversal*) and (any of ($app*) or any of ($sensitive*))
}

Suricata IDS Rule

The following Suricata rule detects path traversal attempts against Sunnet eHRD:

alert http any any -> $HOME_NET any (msg:"CVE-2021-43358 Sunnet eHRD Path Traversal Attempt"; flow:established,to_server; content:"eHRD"; nocase; http_uri; pcre:"/(\.\.\/|\.\.%2f|%2e%2e[\/%5c]|\.\.%5c|%252e%252e)/i"; sid:10043358; rev:1; metadata:cve "2021-43358"; metadata:attack_target "web_server"; metadata:deployment "perimeter"; metadata:former_category "WEB_SERVER"; metadata:signature_severity "High"; metadata:created_at "2025-01-15"; reference:url,nvd.nist.gov/vuln/detail/CVE-2021-43358; classtype:web-application-attack;)

Elastic Detection

The following EQL query detects path traversal patterns in HTTP requests:

sequence by host.name, source.ip with maxspan=5s
  [ network where network.protocol == "http" and
    url.path like~ "*eHRD*" and
    (url.path like~ "*\.\./*" or
     url.path like~ "*\.\.%2f*" or
     url.path like~ "*%2e%2e[%2f|%5c]*" or
     url.path like~ "*\.\.%5c*" or
     url.path like~ "*%252e%252e%252f*")
  ]

Splunk SPL Query

The following Splunk query detects path traversal attempts against Sunnet eHRD:

index=web sourcetype=access_combined 
  uri_path="*eHRD*" 
  AND (uri_path="*../*" OR uri_path="*..%2f*" OR uri_path="*%2e%2e%2f*" 
       OR uri_path="*%2e%2e%5c*" OR uri_path="*..%5c*" OR uri_path="*%252e%252e%252f*")
  AND NOT (uri_path="*/js/*" OR uri_path="*/css/*" OR uri_path="*/images/*")
| stats count by src_ip, dest_ip, uri_path, http_user_agent, _time
| sort - count
| table _time, src_ip, dest_ip, uri_path, http_user_agent, count

Wazuh OSSEC Rule

The following Wazuh rule detects path traversal attempts in web server logs:

<group name="web,">
  <rule id="100433" level="12">
    <decoded_as>json</decoded_as>
    <field name="url">\.\./|\.\.%2f|\.\.%5c|%2e%2e%2f|%2e%2e%5c</field>
    <field name="url">eHRD|ehdr</field>
    <description>CVE-2021-43358 - Sunnet eHRD Path Traversal Attempt</description>
    <group>attack.t1190,attack.t1000,</group>
    <mitre>
      <id>T1190</id>
      <id>T1000</id>
    </mitre>
    <references>
      <url>https://nvd.nist.gov/vuln/detail/CVE-2021-43358</url>
    </references>
    <info type="cve">CVE-2021-43358</info>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 2/4 — CLAIMED — only the CNA (Sunnet) claims a patch exists; this has not been independently verified. The vulnerability may still exist in versions claimed to be fixed.

1) Immediate Mitigations

• Network-level blocking: Deploy or update WAF rules to block path traversal payloads (including URL-encoded variants) at the perimeter. Pay special attention to encoded forms: %2e, %252e, double-encoding, and backslash variants
• Access restriction: Immediately restrict network access to Sunnet eHRD interfaces — move the application behind VPN or zero-trust network access where possible
• Authentication enforcement: If the vulnerable functionality requires authentication in your deployment, ensure all externally accessible pages enforce session validation before processing file-path parameters
• File system hardening: Run the application with the minimum OS privileges necessary. Ensure the web server process cannot read sensitive system files (e.g., /etc/shadow, SSH private keys, application configuration files outside the web root)
• Monitor for exploitation: Deploy the detection rules provided above and review historical logs for potential past exploitation

2) Patch/Upgrade Steps

• Upgrade Sunnet eHRD to version 10 as claimed by the vendor
• Important caveat: The patch is 2/4 confidence, meaning only a single source (the CNA) has claimed a fix, and it has not been independently confirmed. After upgrading:
  • Perform regression testing of file download/upload functionality
  • Verify that path traversal payloads against all file-related parameters are properly blocked
  • Contact Sunnet support to obtain confirmation of the patch specifics and request a security advisory with detailed fix information
• If the vendor cannot provide verifiable patch details, consider compensating controls (WAF rules, reverse proxy filtering) mandatory

3) Long-Term Hardening

• Input validation: Implement a strict allowlist of allowed characters for all URL parameters that reference file paths. Reject any request containing .., %2e, \, %5c, or null bytes
• Canonicalization: Ensure the application canonicalizes file paths before access and verifies the resolved path stays within the intended web root directory
• Architecture improvements: Place Sunnet eHRD behind a reverse proxy that performs URL sanitization before forwarding requests to the application
• Harden HR systems: Since eHRD systems handle sensitive PII, implement additional protections: network segmentation, least-privilege file system access, and regular vulnerability scanning
• Maintain patch hygiene: Establish a process to monitor for new Sunnet advisories and verify vendor claims independently before deploying
• Implement audit logging: Ensure the application logs all file-access operations for forensic analysis

References

1. NVD Entry: CVE-2021-43358 — https://nvd.nist.gov/vuln/detail/CVE-2021-43358
2. CNA: Sunnet (vendor advisory — claims fix in version 10; no public advisory URL available)
3. NVD CVSS Calculator (CVSS v3.1, score 7.5): https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?name=CVE-2021-43358
4. MITRE ATT&CK: Technique T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
5. CWE-22: Improper Limitation of a Pathname to a Restricted Directory: https://cwe.mitre.org/data/definitions/22.html

Known Threat Actor Campaigns / In-the-Wild Exploitation: As of the publication date of this report, CVE-2021-43358 is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog. The EPSS score (0.02294, 81.7% percentile) indicates an elevated likelihood of exploitation relative to the general CVE population, but no specific threat actor campaigns have been publicly attributed. The absence of public PoC code or Nuclei templates suggests exploitation activity, if any, remains low-profile or targeted. Organizations should nonetheless treat this as a high-priority remediation target due to the unauthenticated nature of the vulnerability and the sensitivity of data processed by Sunnet eHRD.

Report generated by Valters IT Security — based on NVD and vendor-supplied data as of January 2025. Patch claims remain unverified; independent validation is recommended before assuming remediation.