CVE-2023-34103 is a high-severity (CVSS 7.3) Cross-site Scripting (XSS) vulnerability in avo. 1 public exploit reference exists, so weaponization risk is real. A fix is available for avo — see the affected versions and patch details below.
Stored XSS (Cross Site Scripting) in html content based fields of avo
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.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-34103.
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-2023-34103 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
avo💎avoReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Some avo fields are vulnerable to XSS when rendering html based content.
Details
During the analysis of the web application, a rendered field was discovered that did not filter JS / HTML tags in a safe way and can be abused to execute js code on a client side. The trix field uses the trix editor in the backend to edit rich text data which basically operates with html tags. To display the stored data in a rendered view, the HasHTMLAttributes concern is used. This can be exploited by an attacker to store javascript code in any trix field by intercepting the request and modifying the post data, as the trix editor does not allow adding custom html or js tags on the frontend.
PoC
Adding javascript in the post request which is used when editing a "post" resource (body is declared as a trix field)
Successful execution of JS code on live demo environment
Impact
Unlike non-persistent XSS, persistent XSS does not require a social engineering phase. Victims of this attack do not need to be tricked into clicking a link or something like that. However, by exploiting such a vulnerability on this particular target, attackers may be able to gain access to accounts that require special protection, such as administrators of the web service, which is what Avo is primarily intended to be used for.
Recommendation
The content of a field that contains html code should be sanitized using the according rails helper which uses a whitelist of known-safe tags and attributes. Also this security consideration should be applied to the “as_html” attribute as well because it may contain user controlled input as well.
https://api.rubyonrails.org/classes/ActionView/Helpers/SanitizeHelper.html
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | avo | all versions | 2.33.3bundle update avo --conservative |
| 💎RubyGems | avo | ≥ 3.0.0.pre1 | No fix |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for avo, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update avo to 2.33.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-34103 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-2023-34103 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-34103. 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-2023-34103 in your dependencies?
O3 Security finds CVE-2023-34103 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.