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SolarWinds Serv-U EUVDEUVD-2026-46289

| CVE-2026-28308 CRITICAL
Authorization Bypass Through User-Controlled Key (CWE-639)
2026-07-21 SolarWinds GHSA-hjp7-x3qv-vqf3
9.1
CVSS 3.1 · Vendor: SolarWinds
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Authenticate as Serv-U domain admin
  2. Delivery
    Manipulate user-controlled object reference (IDOR)
  3. Exploit
    Bypass per-object authorization check
  4. Execution
    Trigger code execution on host
  5. Impact
    Cross scope for lateral movement

Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V8 - Authorization Object-level authorization, IDOR prevention
Exploitation Conditions

Exploitation requires an authenticated Serv-U domain administrator account (CVSS PR:H) reachable over the network (AV:N), with low attack complexity and no user interaction once that access is held; it is fundamentally an insider or post-credential-compromise attack, not remote-unauthenticated. Key limiting factors: the attacker must already hold domain-administrator-level privileges within Serv-U, and impact is explicitly lower on Windows deployments than on Linux, so platform materially changes realistic severity. The absence of a POC or KEV listing further limits near-term opportunistic exploitation.

Impact

The signals are mixed and should be read carefully. The CVSS 3.1 vector (AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H) yields 9.1 mainly from the scope change and triple-high impact, but PR:H means exploitation requires an already-privileged domain administrator account, which sharply narrows the realistic attacker set to insiders or an adversary who has already compromised admin credentials - this is an authorization-boundary escape, not an unauthenticated internet-facing RCE. There is no EPSS score, no POC, and no KEV listing provided, so there is no evidence of active or widespread exploitation; the risk is best characterized as a high-severity privilege-escalation/lateral-movement primitive rather than a mass-exploitation threat. The vendor also explicitly notes lower impact on Windows deployments, so the worst-case CIA profile likely applies to Linux hosts - verify your platform against the SolarWinds advisory. Given Serv-U's history as a target for MFT-focused actors, patching should be prioritized despite the high privilege prerequisite.

Exploit ScenarioDerived

An attacker who has obtained or been granted Serv-U domain administrator credentials logs into the management interface and manipulates a user-controlled object identifier to reference a resource or code path outside their assigned domain, chaining the IDOR into arbitrary code execution on the underlying server. Because the CVSS scope is changed, successful execution can affect resources beyond the vulnerable component, enabling lateral movement - most severely on Linux hosts, with reduced impact on Windows. No public proof-of-concept is available at time of analysis, so an attacker would need to develop the exploit independently.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.
No patch listed yet 0.5% exploitation probability (EPSS)

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AnalysisAIv1 – Jul 21, 2026

Privilege-scoped remote code execution in SolarWinds Serv-U managed file transfer server stems from an insecure direct object reference that lets an authenticated domain administrator reference objects outside their intended authorization boundary to run code on the host. The flaw carries a 9.1 CVSS due to network reach, scope change, and full confidentiality/integrity/availability impact, though the practical bar is high because domain administrator access is a prerequisite, and impact is reduced on Windows deployments. No public exploit is identified at time of analysis and it is not listed in CISA KEV.

RemediationAI

Upgrade Serv-U to the fixed build shipped in the SolarWinds Serv-U 2026-3 release as described in the release notes (https://documentation.solarwinds.com/en/success_center/servu/content/release_notes/servu_2026-3_release_notes.htm) and cross-referenced in the advisory (https://www.solarwinds.com/trust-center/security-advisories/CVE-2026-28308); the exact patched version string is not stated in the provided input, so validate the target build against those pages before rollout. Because exploitation requires domain administrator privileges, the strongest compensating control is to minimize and tightly govern domain-admin accounts in Serv-U - reduce the number of domain administrators, enforce MFA on those accounts, and audit their creation and activity - accepting the trade-off of added administrative friction. Additionally restrict management-plane network access to the Serv-U admin console (bind it to a management VLAN or place it behind a VPN/allowlist) to limit who can reach the privileged interface, monitoring logs for anomalous cross-domain object access; on Windows the vendor-noted lower impact may modestly reduce urgency but does not remove the need to patch.

Affected VersionsENISA

Serv-U 15.5.4 HF1 and below

Affects your stack

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Technical ContextAI · show details

Serv-U is SolarWinds' commercial managed file transfer (MFT) and secure FTP/HTTP/SFTP server, identified by cpe:2.3:a:solarwinds:serv-u:*:*:*:*:*:*:*:*, deployed on both Windows and Linux to move files across FTP, FTPS, SFTP and HTTP(S). The root cause is CWE-639 (Authorization Bypass Through User-Controlled Key / IDOR): the application uses a client-supplied identifier to select an internal object without verifying that the requesting principal is authorized for that specific object. Because Serv-U supports domain-scoped administration, a domain administrator - intended to be confined to a single domain's resources - can manipulate an object reference to reach resources or code paths beyond that domain, and the tagging as an authentication/authorization bypass reflects the missing per-object access check rather than a memory-safety bug.

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Severity by source

Vendor (SolarWinds) PRIMARY 9.1 CRITICAL
AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
vuln.today AI 9.1 CRITICAL

Network-reachable admin interface (AV:N/AC:L) but requires domain administrator privileges (PR:H); IDOR-to-RCE escaping the domain boundary justifies S:C with full C/I/A impact.

3.1 AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L

Primary rating from Vendor (SolarWinds).

CVSS VectorVendor: SolarWinds

Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

DescriptionCVE.org

SolarWinds Serv-U is affected by an insecure direct object reference (IDOR) vulnerability that can lead to remote code execution. Domain administrator access is required. The impact is lower in Windows deployments.

Executive ViewAI

Why It Matters

SolarWinds Serv-U file transfer server contains a critical authorization bypass vulnerability (CVE-2026-28308, CVSS 9.1) enabling authenticated domain administrators to execute arbitrary code beyond their intended authorization scope. Organizations managing sensitive file transfers through Serv-U face potential data theft and service disruption if domain administrator credentials are compromised; this vulnerability directly impacts operational security for enterprises relying on this platform for secure file exchange. The absence of public exploit code and active exploitation provides a window to implement robust interim controls before threat actors develop proof-of-concept tools.

Business Impact: High
Compensating Controls

Restrict domain administrator access to Serv-U via network segmentation and VPN requirements; enforce multi-factor authentication on all administrative accounts; implement real-time audit logging and behavioral anomaly detection for unauthorized object access; establish rapid incident response protocols for Serv-U instances showing exploitation indicators; conduct periodic access reviews and strengthen credential lifecycle management for domain administrators.

Threat Intelligence Overview

EPSS Score
0.5%
Top 58% exploitable
Prevalence
Medium
widely used commercial MFT/FTP server, but not ubiquitous infrastructure
Social Media
1
Sightings
Data Quality
4 sources
Confidence: Medium

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.5%
Patch available No
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact
High

Priority Score

47
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +46
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

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