CVE-2026-33209: Avo Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-762r-27w2-q22j
Share
CWE-79
Published
Advisory Summary

CVE-2026-33209 is a MODERATE cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Avo libraries in the RubyGems ecosystem. The issue involves avo has a xss vulnerability on `return_to` param. Remediation is available by upgrading affected packages to version 3.30.3.

CVE-2026-33209 at a Glance

CVE Identifier CVE-2026-33209
GHSA Identifier GHSA-762r-27w2-q22j
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Avo
Package Ecosystem RubyGems
Published Date
Last Updated

How to Fix CVE-2026-33209

To remediate this vulnerability, upgrade all affected Avo dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

avo fixed: 3.30.3 
Upgrade avo to 3.30.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for avo

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-33209, inspect your project dependencies for Avo:

inspect dependencies for avo

Analyze the terminal output to locate any version of Avo in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.30.3), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Avo, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## Description A reflected cross-site scripting (XSS) vulnerability exists in the `return_to` query parameter used in the avo interface. An attacker can craft a malicious URL that injects arbitrary JavaScript, which is executed when he clicks a dynamically generated navigation button. ## Impact This vulnerability may allow execution of arbitrary JavaScript in the context of the application. Impact varies depending on deployment: - In unauthenticated setups: exploitable via crafted links sent to users - In authenticated setups: limited to authenticated users and requires interaction

CVE-2026-33209 Affected Avo Versions

1 component(s)
Fixed Versions:
3.30.3
Product / Package Ecosystem Affected Versions Fixed Version
avo
gem/avo
RubyGems
< 3.30.3
3.30.3

References

GitHub Advisory / Wiki ADVISORY
https://github.com/avo-hq/avo/security/advisories/GHSA-762r-27w2-q22j
NVD — CVE-2026-33209 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33209
Avo Source Repository REPOSITORY
https://github.com/avo-hq/avo/pull/4330
Security Fix Commit FIX COMMIT
https://github.com/avo-hq/avo/commit/4453d39ddc6309f3bc8ada73ef21e1971112de7d
Avo Source Repository REPOSITORY
https://github.com/avo-hq/avo
Avo Release RELEASE
https://github.com/avo-hq/avo/releases/tag/v3.30.3
Avo Source Repository REPOSITORY
https://github.com/rubysec/ruby-advisory-db/blob/master/gems/avo/CVE-2026-33209.yml

Frequently Asked Questions

What is CVE-2026-33209?
CVE-2026-33209 is a security vulnerability in Avo involving Avo has a XSS vulnerability on `return_to` param under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Avo versions are affected?
Affected versions include releases prior to 3.30.3 across affected packages: avo.
What version fixes CVE-2026-33209?
Upgrading to 3.30.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is avo affected?
Yes, avo is affected in releases prior to 3.30.3. Upgrade your dependency to 3.30.3 or later.
What CWE is associated with CVE-2026-33209?
CVE-2026-33209 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check RubyGems dependencies for CVE-2026-33209?
Run the dependency tree command: 'inspect dependencies for avo'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-762r-27w2-q22j",
  "modified" : "2026-03-25T18:23:10Z",
  "published" : "2026-03-18T17:26:59Z",
  "aliases" : [ "CVE-2026-33209" ],
  "summary" : "Avo has a XSS vulnerability on `return_to` param",
  "details" : "## Description\n\nA reflected cross-site scripting (XSS) vulnerability exists in the `return_to` query parameter used in the avo interface.\n\nAn attacker can craft a malicious URL that injects arbitrary JavaScript, which is executed when he clicks a dynamically generated navigation button.\n\n## Impact\n\nThis vulnerability may allow execution of arbitrary JavaScript in the context of the application.\n\nImpact varies depending on deployment:\n- In unauthenticated setups: exploitable via crafted links sent to users\n- In authenticated setups: limited to authenticated users and requires interaction",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "avo"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.30.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.30.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/avo-hq/avo/security/advisories/GHSA-762r-27w2-q22j"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33209"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/avo-hq/avo/pull/4330"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/avo-hq/avo/commit/4453d39ddc6309f3bc8ada73ef21e1971112de7d"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/avo-hq/avo"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/avo-hq/avo/releases/tag/v3.30.3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/avo/CVE-2026-33209.yml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-18T17:26:59Z",
    "nvd_published_at" : "2026-03-20T23:16:45Z"
  }
}