# CVE-2026-77999: Business logic in J2Store extension for Joomla

> Attackers can forge PayPal callbacks to fraudulently confirm orders or fail others without payment due to flawed IPN validation logic.

- **Severity:** High 8.7 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 3 Sep 2026
- **Updated:** 3 Sep 2026
- **Also known as:** GHSA-ffqf-m6vh-866w

## What is CVE-2026-77999?

CVE-2026-77999 is a high-severity vulnerability in j2commerce.com J2Store extension for Joomla, published on 3 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### 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.

Weakness: CWE-602 (Client-Side Enforcement of Server-Side Security), CWE-472 (External Control of Assumed-Immutable Web Parameter)

## Which versions are affected by CVE-2026-77999?


## How do I fix CVE-2026-77999?

No fix has been published for CVE-2026-77999 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-77999 being exploited?

There is no known exploitation of CVE-2026-77999 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77999 and fix it if it is affected.

What it is: CVE-2026-77999 is a high-severity vulnerability in j2commerce.com J2Store extension for Joomla, published on 3 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-77999 in the wild and no public exploit code.

Affected product: j2commerce.com J2Store extension for Joomla. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-77999/ (Markdown: https://insights.sbomify.com/CVE-2026-77999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77999
- OSV: https://osv.dev/vulnerability/CVE-2026-77999

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-77999/
Summaries are generated and may contain mistakes; the official description above is the record.