CVE-2026-51926
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAn issue in docuForm GmbH FSM Client v.11.11c allows a remote attacker to obtain sensitive information via the login.php component. A vulnerability was identified in the authentication mechanism that allows user enumeration through the login interface. An attacker can differentiate between valid and invalid usernames based on variations in server responses. This information can be leveraged to identify existing accounts and facilitate further attacks, including brute-force or credential stuffing.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceThe FSM Client login.php component exhibits different server responses for valid versus invalid usernames, allowing remote attackers to enumerate existing user accounts. This user enumeration can be chained with brute-force or credential stuffing attacks to compromise accounts.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Locate the FSM Client login.php fileSearch for login.php in the web root or application directory of your FSM Client installation. Common paths include /login.php, /auth/login.php, or /client/login.php.Affected if The login.php file exists and is accessible via HTTP/HTTPS
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Test login response with invalid usernameSubmit a login request with a clearly invalid username (e.g., nonexistentuser123) and a random password. Capture the exact error message returned.Affected if The server returns an error message that indicates whether the username exists versus just reporting invalid credentials
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Test login response with valid username and wrong passwordSubmit a login request using a known-valid username (or test with several guessed usernames) with an intentionally wrong password. Capture this response.Affected if The error message differs from the one returned for a completely invalid username (e.g., 'Invalid password' vs 'User not found')
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Compare HTTP status codes and response timingSend multiple login requests with both valid and invalid usernames. Compare HTTP status codes (e.g., 200 vs 401) and any differences in response body, headers, or timing that could reveal account existence.Affected if Different HTTP status codes are returned, or response content significantly differs between valid and invalid usernames
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Check for username existence hints in responsesReview all login failure responses for any indication of user existence. Look for messages that say 'user does not exist', 'account not found', or similar versus generic 'invalid credentials' messages.Affected if Any response explicitly confirms or denies the existence of a submitted username
You are affected if login.php returns distinguishable responses that allow an attacker to determine whether specific usernames exist in the system, enabling user enumeration attacks.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataModify login.php to return consistent, generic error messages for both invalid usernames and invalid passwords, regardless of account existence. Consider implementing rate limiting or account lockout policies to further mitigate automated enumeration.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-51926 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-51926 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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