CVE-2026-101158

Executive Summary

CVE-2026-101158 is a stored cross-site scripting (XSS) vulnerability in the CloudVision Fileserver upload API caused by missing input validation. An authenticated attacker holding file upload privileges can inject malicious script content that is later rendered in another CloudVision user's browser session. Because the CVSS scope is marked as Changed (S:C) and the UI vector requires victim interaction, successful exploitation can result in full session hijacking with administrative permissions — a high-impact lateral escalation from a low-trust upload role to account takeover.

Technical Analysis

The vulnerability class is CWE-79 (Improper Neutralization of Input During Web Page Generation, i.e., Cross-Site Scripting), specifically the stored (persistent) variant. The affected component is the Fileserver upload API within the CloudVision product.

Mechanism: The upload API fails to validate or sanitize input supplied through the file upload workflow. Because the malicious content is persisted server-side rather than reflected immediately, it becomes stored XSS. When any other CloudVision user subsequently views or interacts with the uploaded resource through the web interface, the injected script executes in the context of that victim's authenticated session.

Key characteristics derived strictly from the NVD description:

• Precondition: The attacker must already be authenticated and must hold file upload privileges. This is not an unauthenticated attack.
• Validation gap: Input validation is described as missing at the upload API layer, meaning the server accepts content it should reject or neutralize.
• Persistence: The payload is stored (persistent XSS), so exploitation does not require the attacker to lure the victim to a malicious link at attack time — the payload waits in the application.
• Scope change: The CVSS vector includes S:C, indicating the vulnerable component's compromise can affect resources beyond its security scope — here, the victim user's session and privileges.
• User interaction: UI:R indicates the victim must take some action (opening/rendering the uploaded content) for execution to occur.

No specific API endpoint paths, parameter names, function names, or code-level constructs are provided in the CVE description. Accordingly, this report describes the attack at the vulnerability-class level and does not fabricate implementation details. A public PoC, exploit code, or Nuclei template is not available. The exact affected version range is not specified in the supplied data, and no OSV packages are listed.

Exploitation Scenarios

Attack chain inferred strictly from the vulnerability class and the constraints in the NVD description. No public PoC is available; the following is a class-level reconstruction.

1. Reconnaissance / target identification. The attacker identifies an exposed CloudVision instance and confirms the presence of the Fileserver upload API. The attacker must possess valid low-privilege credentials that include file upload privileges — this is the required foothold.

2. Triggering the flaw. Using the authenticated upload privileges, the attacker submits content to the Fileserver upload API. Because the API omits input validation, content containing active scripting is accepted and stored without neutralization. No specific request format or parameter names are documented, so the exact payload delivery format cannot be stated.

3. Execution. The stored content is persisted on the server. When a legitimate CloudVision user later views or opens the uploaded resource in the web interface (the UI:R interaction requirement), the embedded script executes within that victim's browser in the origin/context of the CloudVision application.

4. Post-exploitation impact. The executed script runs as the victim, enabling session hijacking — theft of session tokens or cookies, and performance of actions as the victim. Per the CVSS impact metrics (C:H/I:H/A:H) and the description, this can grant the attacker full access to the victim's account, potentially including administrative permissions. The scope change (S:C) reflects the pivot from the attacker's low-privilege upload context to the victim's higher-privilege session.

Impact Assessment

• Confidentiality (C:H): Full loss of confidentiality for the victim's session context; the attacker can read data accessible to the hijacked account.
• Integrity (I:H): Full loss of integrity — the attacker can act as the victim, including administrative operations.
• Availability (A:H): Full availability impact within the affected session/scope.
• Scope (S:C): The compromise crosses a security boundary from the attacker's upload role to the victim's user account.
• Attack Vector (AV:N) / Complexity (AC:L): Remotely reachable and low complexity.
• Privileges Required (PR:H): Requires authenticated, upload-capable access — this limits the attacker population but does not eliminate the risk, since such roles are commonly delegated.
• User Interaction (UI:R): A victim must render the stored content, meaning exploitation can be delayed and stealthy.

Business impact: For an organization running CloudVision, a successful attack can escalate a limited upload role into takeover of other users' sessions, including administrators. Administrative account hijacking in a network management platform can translate into broad control over monitored/ managed infrastructure, making this a high-priority operational risk. Blast radius extends to any CloudVision user who views the injected content, particularly privileged operators.

Detection Guidance

Sigma Rule

title: Potential Stored XSS Payload Upload to CloudVision Fileserver API
id: 6f2a2c1e-9d3b-4a7e-b1c2-8a9f0e5d7c31
status: experimental
description: Detects upload requests to the CloudVision Fileserver upload API containing script markup indicative of stored XSS (CVE-2026-101158).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-101158
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_uri:
    cs-uri-stem|contains:
      - '/fileserver'
      - '/upload'
  selection_payload:
    - cs-uri-query|contains:
        - '<script'
        - 'javascript:'
        - 'onerror='
        - 'onload='
        - '%3Cscript'
    - cs-uri-query|contains|all:
        - '<'
        - 'script'
  condition: selection_uri and selection_payload
falsepositives:
  - Legitimate uploads of files legitimately containing HTML/JS content
level: high
tags:
  - attack.t1059.007
  - cve.2026.101158

YARA Rule

rule CVE_2026_101158_Stored_XSS_Payload
{
    meta:
        description = "Detects stored XSS payload artifacts uploaded via CloudVision Fileserver upload API (CVE-2026-101158)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-101158"
        date = "2026-01-01"
        severity = "high"

    strings:
        $s1 = "<script" ascii nocase
        $s2 = "</script>" ascii nocase
        $s3 = "onerror=" ascii nocase
        $s4 = "onload=" ascii nocase
        $s5 = "javascript:" ascii nocase
        $s6 = "document.cookie" ascii nocase
        $s7 = "fetch(" ascii nocase
        $s8 = "XMLHttpRequest" ascii nocase

    condition:
        (2 of ($s1, $s2, $s3, $s4, $s5)) or
        (1 of ($s1, $s3, $s4, $s5) and 1 of ($s6, $s7, $s8))
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-101158 Potential Stored XSS Upload to CloudVision Fileserver API"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"upload"; nocase; http.request_body; content:"<script"; nocase; sid:2026101158; rev:1; reference:cve,2026-101158; classtype:web-application-attack; metadata:created_at 2026_01_01, updated_at 2026_01_01;)

Elastic Detection

sequence by user.name, source.ip with maxspan=5m
  [ network where network.protocol == "http" and http.request.method == "POST"
      and wildcard(http.request.body, "*<script*") ]
  [ network where network.protocol == "http" and http.request.method == "GET"
      and wildcard(url.path, "*fileserver*") ]

Splunk SPL Query

index=web sourcetype=access_combined OR sourcetype=nginx
| eval payload = lower(coalesce(uri_query, request_body, ""))
| where (match(uri_path, "(?i)fileserver|upload"))
    AND (like(payload, "%<script%") OR like(payload, "%javascript:%")
         OR like(payload, "%onerror=%") OR like(payload, "%onload=%")
         OR like(payload, "%document.cookie%"))
| stats count values(uri_path) as paths values(src_ip) as sources by user, src_ip
| where count > 0

Wazuh OSSEC Rule

<group name="web,cve-2026-101158,">
  <rule id="101158" level="12">
    <if_sid>31100</if_sid>
    <id>^POST$</id>
    <url>fileserver|upload</url>
    <match>&lt;script|javascript:|onerror=|onload=|document.cookie</match>
    <description>CVE-2026-101158: Possible stored XSS payload uploaded to CloudVision Fileserver API</description>
    <mitre>
      <id>T1059.007</id>
    </mitre>
    <group>web_attack,xss,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations:

   • Restrict and audit who holds file upload privileges in CloudVision; enforce least privilege.
   • Apply output encoding / input sanitization at the web application or reverse proxy layer where feasible (e.g., content security headers, disallowing inline script execution).
   • Deploy a Web Application Firewall rule set targeting script markup in upload requests as a compensating control.
   • Monitor web logs for upload requests containing script markup (see Detection Guidance above).

2. Patch/upgrade steps:

   • No vendor fix, workaround, or affected version information is currently available from tracked sources. Monitor the vendor (Arista CloudVision) advisory channels and the NVD entry for CVE-2026-101158 for an official patch or version guidance. Do not assume any version is fixed until the vendor publishes an advisory.

3. Long-term hardening:

   • Enforce strict server-side input validation and output encoding for all fileserver/upload content.
   • Implement a Content Security Policy that blocks inline and unauthorized script execution.
   • Adopt session protection controls (HttpOnly, Secure, SameSite cookies) to reduce hijacking impact.
   • Require re-authentication or step-up for administrative actions to limit post-hijack escalation.

References

• NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-101158
• CWE-79 (Improper Neutralization of Input During Web Page Generation — Cross-site Scripting): https://cwe.mitre.org/data/definitions/79.html
• MITRE ATT&CK T1059.007 (Command and Scripting Interpreter: JavaScript): https://attack.mitre.org/techniques/T1059/007/
• CISA Known Exploited Vulnerabilities Catalog: Not listed for this CVE (verified: CISA KEV = NO)
• Vendor advisory: Not available at time of writing. No threat actor campaign or exploit-in-the-wild evidence has been identified for CVE-2026-101158 in the provided data.