CVE-2021-26598 is a medium-severity (CVSS 5.3) vulnerability in impresscms/impresscms. 4 public exploit references exist, so weaponization risk is real. A fix is available for impresscms/impresscms — see the affected versions and patch details below.
Incorrect Access Control in ImpressCMS
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-26598 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
impresscms/impresscmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
ImpressCMS before 1.4.3 has Incorrect Access Control because include/findusers.php allows access by unauthenticated attackers (who are, by design, able to have a security token).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | impresscms/impresscms | all versions | 1.4.3composer require impresscms/impresscms:^1.4.3 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
ImpressCMS before 1.4.3 has Incorrect Access Control because include/fin…
ImpressCMS before 1.4.3 has Incorrect Access Control because include/fin…
ImpressCMS before 1.4.3 has Incorrect Access Control because include/fin…
ImpressCMS before 1.4.3 has Incorrect Access Control because include/fin…
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for impresscms/impresscms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update impresscms/impresscms to 1.4.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-26598 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-26598 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-26598. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
How to detect CVE-2021-26598
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-26598 -u https://target- Template
- ImpressCMS <1.4.3 - Incorrect Authorization
- Severity
- medium
- Impact
- An attacker can bypass authorization and gain unauthorized access to sensitive information or perform unauthorized actions.
- Remediation
- Upgrade to ImpressCMS version 1.4.3 or later to fix the vulnerability.
Template by ProjectDiscovery nuclei-templates (gy741, pdteam), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2021-26598 in your dependencies?
O3 Security finds CVE-2021-26598 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.