VulnerabilityPublished 15 Sep 2026Updated 21 Sep 2026

CVE-2026-91981: vikunja · Information Exposure

Affects vikunjaSource CVE Database V5

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Not known to be exploited · CVSS 4.3 Medium : upgrade to 2.6.0 when convenient.

Data as of 30 Oct 2026, 20:25 UTC

CVSS 3.1 base score

4.3Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 23% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.6.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 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 fix involves updating the v2 user-search endpoints to reject link-share tokens by resolving the caller with GetFromAuth, matching the behavior of the v1 endpoints. If you cannot patch yet, restrict distribution of link-share tokens and monitor for unauthorized access attempts.

Description

### Summary A link-share token, the credential you hand out to let someone view a shared project, can call the v2 user-search endpoints, which it was never meant to reach. The v1 versions of the same endpoints correctly reject link-share tokens; the v2 versions don't. As a result, anyone with a share link can list every member of the shared project (and its parent projects), and can test whether any username exists anywhere on the instance. ### Details Two endpoints are affected: `GET /api/v2/projects/{id}/users/search` only checks project.CanRead, which a link share satisfies on its own project. With no parameter it returns the full user list, walking up the parent-project chain. `GET /api/v2/users?q=<name>` is a global search. It needs a query term, but any term works as an existence oracle: a hit confirms the username exists somewhere on the instance and returns the display name. Emails are correctly stripped from these responses, so the exposure is limited to identities (usernames and display names), but that's still an instance-wide directory that a share-link holder should never see. The fix is to resolve the caller with GetFromAuth in both handlers, so link-share tokens are rejected the same way v1 already rejects them. ### PoC 1. Get a link-share token. With any account that owns a project, create a read-only link share and note the hash, then exchange it: ``` POST /api/v1/shares/<hash>/auth {"password":""} ``` The response contains a token, a link-share JWT. 2. Confirm v1 blocks it (the fixed behavior). With that token: ``` GET /api/v1/projects/<id>/projectusers Authorization: Bearer <link_share_token> ``` → rejected: the token isn't a user token. 3. Now the vulnerable v2 endpoints, same token: ``` GET /api/v2/projects/<id>/users/search Authorization: Bearer <link_share_token> ``` → 200, full list of everyone with access to the project and its parents (id, username, name). ``` GET /api/v2/users?q=admin Authorization: Bearer <link_share_token> ``` → 200, a non-empty result confirms the username exists on the instance. Iterate q over a wordlist to enumerate accounts. ### Impact Information disclosure. A link share is a low-trust credential meant to expose one project's contents; here it also exposes the membership of that project's parents and lets the holder probe for any username across the whole instance. Since share links are often forwarded or semi-public, this hands an untrusted recipient a map of internal users and a username-validation oracle useful for phishing and credential stuffing. No account is required beyond possessing a share link. Emails are not exposed.

Impact

This vulnerability leads to information disclosure of usernames and display names across the entire instance to anyone possessing a link-share token. This exposure can facilitate targeted phishing and credential stuffing attacks by providing a validated list of internal users and a username existence oracle. No authentication beyond the share link is required, increasing the risk of unauthorized information gathering.

Summary

The vulnerability (CVE-2026-91981) in go-vikunja vikunja arises because the v2 user-search API endpoints do not properly reject link-share tokens, unlike their v1 counterparts. Specifically, the GET /api/v2/projects/{id}/users/search endpoint only checks if the token has project read access, which a link-share token satisfies, allowing it to return the full user list for the project and its parent projects. The GET /api/v2/users?q=<name> endpoint allows global username existence checks. Emails are not disclosed, but usernames and display names are exposed. The issue is due to missing proper authentication resolution in the v2 handlers, which can be fixed by applying the same token rejection logic as v1.

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Affected software

Description

AI analysisMachine-generated, updated 9 Oct 2026, 22:47 UTC

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