Vikunja before 2.6.0 Authentication Bypass via CalDAV BasicAuth

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Vikunja before 2.6.0 contains an authentication bypass vulnerability in CalDAV BasicAuth endpoints that lack rate limiting protection. Remote unauthenticated attackers can issue unbounded credential-guessing requests against /dav, /.well-known, and /feeds routes to bypass the instance's anti-brute-force controls and compromise password-only accounts.

Source published

15 Sep 2026 15:18:23 UTC

Source modified

15 Sep 2026 15:55:04 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Vikunja before 2.6.0 contains an authentication bypass vulnerability in CalDAV BasicAuth endpoints that lack rate limiting protection. Remote unauthenticated attackers can issue unbounded credential-guessing requests against /dav, /.well-known, and /feeds routes to bypass the instance's anti-brute-force controls and compromise password-only accounts.

Source published

Sep 15, 2026, 3:18:23 PM (timezone not stated)

Source modified

Sep 15, 2026, 3:55:04 PM (timezone not stated)

Observed here

7 Nov 2026 15:25:00 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Vikunja before 2.6.0 contains an authentication bypass vulnerability in CalDAV BasicAuth endpoints that lack rate limiting protection. Remote unauthenticated attackers can issue unbounded credential-guessing requests against /dav, /.well-known, and /feeds routes to bypass the instance's anti-brute-force controls and compromise password-only accounts.

Source published

15 Sep 2026 16:17:54 UTC

Source modified

16 Sep 2026 20:16:09 UTC

Observed here

25 Oct 2026 16:19:22 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Primary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

### Summary The `/dav`, `/.well-known`, and `/feeds` groups are registered on the root Echo instance with only BasicAuth and no rate limiter. CalDAV BasicAuth accepts the plain account password, so password guessing over `/dav` is unbounded and never returns 429, while `/api/v1/login` is throttled from the tenth attempt. The only anti-brute-force control on the instance is therefore bypassable. ### Details `pkg/routes/routes.go` (~lines 238-249) registers `/.well-known`, `/dav`, and `/feeds` with `middleware.BasicAuth(...)` and nothing else; `registerCalDavRoutes` adds no limiter. `pkg/routes/caldav/auth.go` (~lines 88-93) falls through to `user.CheckUserCredentials` with the plain account password when no CalDAV token matches. In contrast, `/register`, `/login`, etc. are wrapped by `unauthRateLimit()` — an unconditional 10/min/IP pre-auth floor that ignores `ratelimit.enabled` (default false). TOTP-enabled accounts and bot users are correctly refused, so this targets password-only accounts. ### PoC (verified at runtime against v2.5.0) ``` POST /api/v1/login x25 wrong passwords -> 429 from attempt 2 (throttled) PROPFIND /dav/principals/{user}/ x60 wrong passwords -> 401 x60, 429 x0 GET /feeds/notifications.atom x30 wrong passwords -> 401 x30, 429 x0 PROPFIND /dav/... with correct password -> 207 (proves the 401s are real auth failures) ``` ### Impact The anti-brute-force floor guarding `/login` is entirely absent on `/dav`, `/feeds`, and `/.well-known`, giving an unbounded credential-guessing surface against account passwords. (bcrypt caps throughput to a few guesses/second, but nothing caps the number of attempts.) Reported as an authentication-control bypass, not a DoS. ### Fix Apply the unconditional pre-auth rate-limit floor to the `/dav`, `/.well-known`, and `/feeds` groups.

Source published

9 Oct 2026 20:52:04 UTC

Source modified

19 Oct 2026 21:40:52 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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Publisher rating · MODERATE

### Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-m469-88xx-8rx2. This link is maintained to preserve external references. ### Original Description Vikunja before 2.6.0 contains an authentication bypass vulnerability in CalDAV BasicAuth endpoints that lack rate limiting protection. Remote unauthenticated attackers can issue unbounded credential-guessing requests against /dav, /.well-known, and /feeds routes to bypass the instance's anti-brute-force controls and compromise password-only accounts.

Source published

15 Sep 2026 18:32:30 UTC

Source modified

9 Oct 2026 21:00:06 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Publisher rating · HIGH

Vikunja: CalDAV and feeds BasicAuth endpoints have no rate limit, bypassing the anti-brute-force floor on account passwords in code.vikunja.io/api. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: code.vikunja.io/api before v2.6.0.

Source published

19 Oct 2026 21:08:26 UTC

Source modified

19 Oct 2026 21:31:35 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.