VulnerabilityPublished 15 Sep 2026Updated 17 Sep 2026

CVE-2026-91972: vikunja · Improper Restriction of Excessive Authentication Attempts

Affects vikunjaSource CVE Database V5

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Not known to be exploited · CVSS 8.7 High : upgrade to 2.6.0 soon.

Data as of 30 Oct 2026, 20:25 UTC

CVSS 4.0 base score

8.7High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.6% chance of exploitation in 30 days – higher than 50% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.6.0

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 15 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade vikunja and github.com/go-vikunja/vikunja to 2.6.0.

Affected software

Product	Affected	Fixed in
go-vikunjavikunja	Affected <2.6.0	Fixed in 2.6.0
Gogithub.com/go-vikunja/vikunja`pkg:golang/github.com/go-vikunja/vikunja`Other threats	Affected <2.6.0	Fixed in 2.6.0

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AI-suggested

The vendor's recommended fix is to apply the unconditional pre-auth rate-limit floor ('unauthRateLimit()') to the v2 public route group, aligning it with v1 behavior. If you cannot patch yet, users should consider implementing custom rate-limiting controls on v2 pre-auth endpoints to mitigate abuse.

Description

### Summary `registerAPIRoutesV2` never applies the unconditional pre-auth rate-limit floor (`unauthRateLimit()`) to the v2 public routes — it passes that limiter only to `/api/v2/ws` — and otherwise relies on `setupRateLimit`, which registers nothing when `ratelimit.enabled` is false (the default). So on a stock install every v2 pre-auth endpoint (login, register, password-reset token, oauth token) is unthrottled, while its v1 twin is throttled. ### Details `unauthRateLimit()` -> `perMinuteIPRateLimit("noauth", RateLimitNoAuthRoutesLimit)` (`pkg/routes/rate_limit.go`, ~lines 100-118) is an unconditional per-IP floor (default 10/60s) that deliberately ignores `RateLimitEnabled`, which is why v1's pre-auth routes are throttled even with the global limiter off. v1 applies it: `ur := a.Group(""); ur.Use(unauthRateLimit())` (`pkg/routes/routes.go` ~line 459). `registerAPIRoutesV2` (~lines 405-431) passes the `unauthRateLimit()` instance only to `/api/v2/ws`; its auth routes get only `setupRateLimit(a, ...)`, which is config-gated and registers nothing by default. ### PoC (verified at runtime against v2.5.0) ``` POST /api/v1/login x25 -> 429 from attempt 5 POST /api/v2/login x25 -> 403 x25, 429 x0 POST /api/v1/user/password/token -> 429 (throttled) POST /api/v2/user/password/token x20 -> 404 x20, 429 x0 ``` Request bodies are byte-identical across versions (shared `user.Login` / `user.PasswordTokenRequest`). Both v2 endpoints reach their handlers (403/404, not route-404), so the comparison is valid. ### Impact The pre-auth rate-limit floor — the instance's only default anti-brute-force / anti-abuse control — is absent on all v2 public endpoints. Enables unbounded credential guessing, account-enumeration probing, and password-reset flooding on a default install. Reported as an authentication-control bypass, not a DoS. ### Fix Apply `unauthRateLimit()` to the v2 public route group, matching v1.

Impact

The absence of the default pre-auth rate-limit on v2 public endpoints removes the only default anti-brute-force and anti-abuse control on a stock installation. This allows attackers to perform unlimited credential guessing attempts, probe for valid accounts, and flood password-reset token requests without restriction. This can lead to compromised accounts or account lockout scenarios. The vulnerability does not cause denial-of-service but significantly weakens authentication controls.

Summary

The vulnerability arises because the function 'registerAPIRoutesV2' does not apply the unconditional pre-auth rate-limit floor ('unauthRateLimit()') to v2 public routes except for '/api/v2/ws'. Instead, it relies on 'setupRateLimit', which is disabled by default, resulting in no throttling on v2 pre-auth endpoints such as login, register, password-reset token, and OAuth token. In contrast, v1 endpoints apply 'unauthRateLimit()' unconditionally, enforcing a default per-IP limit of 10 requests per 60 seconds. Proof of concept testing against v2.5.0 confirmed that v2 endpoints allow many more requests without triggering rate-limit responses, enabling abuse. The vulnerability is classified as an authentication-control bypass rather than a denial-of-service issue. The recommended fix is to apply 'unauthRateLimit()' to the v2 public route group to match v1 behavior.

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What to do

Affected software

Description

AI analysisMachine-generated, updated 9 Oct 2026, 22:49 UTC

Technical details

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