CVE-2026-55554
CVE-2026-55554 is a Improper Input Validation vulnerability in dompdf/dompdf. O3 Security confirms whether CVE-2026-55554 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Dompdf: Chroot Validation Bypass
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-2026-55554.
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.
Real-World Exposure
dompdf/dompdfReal-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
Dompdf is an HTML to PDF converter for PHP. In versions 3.15 and prior, the validateLocalUri() method enforces chroot boundaries with a strpos() prefix check after normalizing paths with realpath() . Because normalization strips the trailing directory separator from $chrootPath , the check only verifies that $chrootPath is a string prefix of $realfile, so a chroot of /var/www also matches sibling directories like /var/www2 , /var/www-admin, or /var/www_backup. An attacker who controls part of the rendered HTML could exploit this to escape the chroot and read sensitive files outside the allowed directory. This issue has been fixed in version 3.16.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | dompdf/dompdf | all versions | 3.1.6 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dompdf/dompdf. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update dompdf/dompdf to 3.1.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55554 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 pinpoints whether CVE-2026-55554 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-55554. 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-2026-55554 in your dependencies?
O3 detects CVE-2026-55554 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.