CyberSecBulletin
CVE-2026-53644NVD status: Deferred

FOSSBilling: Authorization Bypass Through User-Controlled Key

Published Updated By the CyberSecBulletin desk

CVE-2026-53644 is a high-severity authorization bypass through user-controlled key vulnerability in FOSSBilling, with a CVSS 4.0 base score of 8.6 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected FOSSBilling versions: >= 0.5.3, < 0.8.0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.39% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Check which version of FOSSBilling you run against the affected versions below, and install the vendor's latest release.
  2. Read the advisory on github.com for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
FOSSBillingFOSSBilling>= 0.5.3, < 0.8.0Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Attack requirements
NoneThe attack does not depend on a particular deployment or configuration.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Confidentiality (vulnerable system)
HighSerious loss of confidentiality on the vulnerable system.
Integrity (vulnerable system)
HighSerious loss of integrity on the vulnerable system.
Availability (vulnerable system)
NoneNo loss of availability on the vulnerable system.
Confidentiality (other systems)
NoneNo loss of confidentiality on systems beyond the vulnerable one.
Integrity (other systems)
NoneNo loss of integrity on systems beyond the vulnerable one.
Availability (other systems)
NoneNo loss of availability on systems beyond the vulnerable one.

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. Scored by CNA (github.com).

Official description

FOSSBilling is a free, open-source billing and client management system. Versions 0.5.3 through 0.7.2 allow authenticated clients to both read and reset API key service secrets for orders that are no longer in an `active` state (e.g., `suspended`, `canceled`). The root cause is missing order-state validation in two client API endpoints, despite an `isActive()` helper already existing in the `Serviceapikey` module and the frontend UI correctly gating access on `order.status == 'active'`. Version 0.8.0 contains a fix. Some workarounds are available. If the `Serviceapikey` module is not needed, uninstall it to remove the affected endpoints. One may also use a reverse proxy or WAF to restrict access to `/api/client/order/service` and `/api/client/serviceapikey/reset` based on application-level order-state logic.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Authorization Bypass Through User-Controlled Key

The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

How developers prevent this class of flaw

  • For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
  • Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
  • Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.

More Authorization Bypass Through User-Controlled Key vulnerabilities (CWE-639)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in FOSSBilling

All FOSSBilling vulnerabilities

Recent Authorization Bypass Through User-Controlled Key vulnerabilities

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