CVE-2026-42612 is a high-severity (CVSS 8.5) Cross-site Scripting (XSS) vulnerability in getgrav/grav. A fix is available for getgrav/grav — see the affected versions and patch details below.
Grav: Publisher-Level Stored XSS via Unquoted Event Attributes
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42612.
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-2026-42612 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 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
getgrav/gravReal-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
Summary
A stored Cross-Site Scripting (XSS) vulnerability in getgrav/grav allows publisher-level accounts to execute arbitrary JavaScript. The issue arises from a blacklist bypass in the detectXss() function when handling unquoted HTML event attributes.
Details
The detectXss() function relies on a blacklist pattern to filter malicious attributes. The specific regex pattern used to match on* events is flawed:
'on_events' => '#(<[^>]+[a-z\x00-\x20\"\'\/])(on[a-z]+|xmlns)\s*=[\s|\'\"].*[\s|\'\"]>#iUu'
This pattern fails to properly identify on* event handlers that are constructed without quotation marks. This allows an attacker to completely bypass the filter. Note: It is highly recommended to replace this blacklist approach with a robust, established HTML sanitization library.
PoC
An attacker with publisher-level access can reproduce this by injecting the following payload into any vulnerable content field:
<img src=x onerror=eval(atob(/YWxlcnQoZG9jdW1lbnQuY29va2llKQ/.source))>
Execution Details:
The onerror event is written without quotes to bypass the regex. Because unquoted attributes are restricted in their character usage (e.g., the = symbol cannot be used easily), the payload leverages atob() and regex .source to decode the base64 string YWxlcnQoZG9jdW1lbnQuY29va2llKQ (which translates to alert(document.cookie)). The atob() function conveniently auto-completes the necessary = padding for the base64 string.
Impact
- Vulnerability Type: Stored Cross-Site Scripting (XSS)
- Impacted Parties: Any user (including administrators) who views the compromised content published by the attacker.
- Consequences: Attackers can execute malicious scripts in a victim's browser, leading to session hijacking (cookie theft), unauthorized actions.
Maintainer note — fix applied (2026-04-24)
Fixed in Grav core on the 2.0 branch: commit 5a12f9be8 — will ship in 2.0.0-beta.2.
What changed: the on_events regex in Security::detectXss() no longer requires quotes or whitespace around =. The previous form:
'on_events' => '#(<[^>]+[\s\x00-\x20\"\'\/])(on\s*[a-z]+|xmlns)\s*=[\s|\'\"].*[\s|\'\"]>#iUu'
required [\s|'"] immediately after the =, so <img src=x onerror=alert(1)> slid past. The new regex drops the value-matching tail entirely and just flags the presence of an on*= attribute anywhere inside a tag:
'on_events' => '#<[^>]*?[\s\x00-\x20\"\'\/](on\s*[a-z]+|xmlns)\s*=#iu'
Detecting the attribute name + = is enough for a tripwire — the trade-off is occasional false positives on legitimate attribute values containing on*= substrings, which the maintainer can hand-approve.
This same regex bypass was the detection-layer half of GHSA-c2q3-p4jr-c55f and GHSA-w8cg-7jcj-4vv2; the fix here knocks both down.
Files:
system/src/Grav/Common/Security.php.tests/unit/Grav/Common/Security/DetectXssTest.php— 18 cases: unquoted PoCs, quoted-form regression, safe-content negatives.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | getgrav/grav | all versions | 2.0.0-beta.2composer require getgrav/grav:^2.0.0-beta.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for getgrav/grav, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update getgrav/grav to 2.0.0-beta.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42612 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-2026-42612 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42612. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-42612 in your dependencies?
O3 Security finds CVE-2026-42612 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.