Grav: XSS Blueprint Validation Bypass via Twig String Concatenation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source

EPSS

• CVE-2026-61453: 0.20% estimated exploitation activity in the next 30 days; percentile 9.34 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The XSS blueprint validator (Security::detectXss()) runs on the raw page content before Twig processing. An attacker can use Twig's string concatenation operator (~) to dynamically construct an event handler name at render time. The validator sees {{ "on" ~ "error" }} - a harmless Twig expression - and allows the content. After Twig processes the template, the output contains <img src=1 onerror=alert(1) which is rendered via {{ content|raw }} and executes in the victim's browser. --- Details The two-stage attack exploits the separation between validation and rendering: Stage 1 - what the XSS validator sees (raw page content): The detectXss() function scans this string. The onevents regex looks for <[^]?\s\x00-\x20\"\'\/\s= inside HTML tags. In {{ x }}, the { character is not in the boundary set [\s\x00-\x20\"\'\/], and x is not on. No match - passes validation. Stage 2 - what Twig produces (after rendering): The validator never re-inspects Twig output. The theme template…

Published by the source

16 Sep 2026, 22:13 UTC

Last modified by the source

16 Sep 2026, 22:30 UTC

Source last checked

26 Oct 2026, 14:53 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-2c4f-86xc-cr74

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-2c4f-86xc-cr74

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# Patch Next advisory brief: CVE-2026-61453

Advisory: Grav: XSS Blueprint Validation Bypass via Twig String Concatenation
IDs: CVE-2026-61453, GHSA-2c4f-86xc-cr74
Record: https://patchnext.com/advisories/cve-2026-61453 (revision 3, source checked 26 Oct 2026, 14:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: getgrav/grav 2.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist getgrav/grav: affected >= 2.0.0, <= 2.0.0; fixed in 2.0.1

## Suggested inspection (read-only)
- Packagist getgrav/grav: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on getgrav/grav.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-2c4f-86xc-cr74 (OSV record GHSA-2c4f-86xc-cr74 lists affected ranges: Packagist getgrav/grav >=2.0.0 <2.0.1 (fixed))
- Verified: https://github.com/advisories/GHSA-2c4f-86xc-cr74 (GitHub-reviewed advisory GHSA-2c4f-86xc-cr74 lists affected ranges: Packagist getgrav/grav >=2.0.0 <=2.0.0)

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