J2Store extension for Joomla: External Control of Assumed-Immutable Web Parameter
CVE-2026-77999 is a high-severity external control of assumed-immutable web parameter vulnerability in J2Store extension for Joomla from J2commerce.com, with a CVSS 4.0 base score of 8.7 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected J2Store extension for Joomla versions: 1.0.0-3.3.21; 4.0.0-4.0.21; 4.1.0-4.1.6. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.43% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of J2Store extension for Joomla you run against the affected versions below, and install the vendor's latest release.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| J2commerce.com | J2Store extension for Joomla | 1.0.0-3.3.21; 4.0.0-4.0.21; 4.1.0-4.1.6 | Not 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
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Confidentiality (vulnerable system)
- NoneNo 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:N/UI:N/VC:N/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 (joomla.org).
Official description
Joomla Extension - j2commerce.com - Unauthenticated PayPal callback forgery leading to order confirmation fraud in J2Store 1.0.0-3.3.21, 4.0.0-4.0.21, 4.1.0-4.1.6 - The PayPal IPN listener's signature check (`_validateIPN()`) accepted `UNVERIFIED` and any non-`INVALID` response as valid, made its verification request with `CURLOPT_SSL_VERIFYPEER` disabled, and stored its verdict in a field nothing downstream ever checked — so processing continued regardless of the outcome. Separately, the paid-amount comparison only ran when `mc_gross` was a positive number; omitting the field from the POST body (`floatval(null) == 0`) skipped the check entirely. Combined with a merchant-configured `receiver_email` and a sequential, enumerable order id read from the `custom` field, an anonymous POST was enough to move a pending order straight to `CONFIRMED` with no payment, or force another customer's pending order to `FAILED`. `paypalv2.php` performed no amount check under any circumstances.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: External Control of Assumed-Immutable Web Parameter
The web application does not sufficiently verify inputs that are assumed to be immutable but are actually externally controllable, such as hidden form fields.
How developers prevent this class of flaw
- Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
More External Control of Assumed-Immutable Web Parameter vulnerabilities (CWE-472)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
References
Other references
Other vulnerabilities in J2Store extension for Joomla
- 8.7 High severity
- 8.7 High severity
- 8.7 High severity
- 7.1 High severity
- 9.5 Critical severity
- 7.1 High severity
Recent External Control of Assumed-Immutable Web Parameter vulnerabilities
- 7.7 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 8.3 High severity
- 9.6 Critical severity
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