CVE-2023-34103 is a high-severity (CVSS 7.3) Cross-site Scripting (XSS) vulnerability in avo. 1 public exploit or proof-of-concept reference is indexed, 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
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
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 |
Affected Products
avoavohqResearch 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
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2023-34103 in your dependencies?
Find it across RubyGems, including transitive dependencies.