CVE-2026-76216VulnerabilityPublished 9 Oct 2026Updated 27 Oct 2026

code.vikunja.io/api · Vikunja: Link-share principal-type confusion enables cross-account team removal, bot takeover, and roster disclosure

Affects code.vikunja.io/apiSource GCVE Database

Mentioned vulnerabilities

CVE-2026-68581

Authoritative record:CVE-2026-76216· High 7.7

Not known to be exploited · CVSS 7.7 High : upgrade to 2.5.0 soon.

Data as of 27 Oct 2026, 16:27 UTC

CVSS 4.0 base score

7.7High

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

Patch: Available – fixed in 2.5.0

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

Attack Vector: Network
Attack Complexity: High
Attack Requirements: Present
Privileges Required: Low
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: High
Vulnerable system availability: High
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: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
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: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
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 19 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 code.vikunja.io/api to 2.5.0.

Affected software

Product	Affected	Fixed in
Gocode.vikunja.io/api	Affected <2.5.0	Fixed in 2.5.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

## Summary Vikunja's `web.Auth` interface (`pkg/web/web.go`, single method `GetID() int64`) is satisfied by BOTH `*user.User` and `*models.LinkSharing`. A link-share's `GetID()` returns the **raw positive** `share.ID` (`pkg/models/link_sharing.go:83-85`), which lives in the same positive autoincrement ID space as `users.id`. The safe negated form `getUserID() = share.ID * -1` (`link_sharing.go:126-128`) exists but is NOT used at three permission sinks. As a result, a link-share principal with id `N` — which should have zero authority over teams or bot users — is treated as the *user* whose `users.id == N` at three permission checks that lack the `a.(*LinkSharing)` guard their sibling methods have. This is the same principal-type-confusion class as CVE-2026-68581 (GHSA-vvcv-vpph-h844), but at three code paths that advisory/fix never touched. ## Root Cause `web.Auth` is a one-method interface (`GetID() int64`). `*LinkSharing.GetID()` returns the raw positive share id. Three permission methods compare this raw id directly and omit the link-share type guard used elsewhere in the same files: 1. **`TeamMember.CanDelete`** (`pkg/models/team_members_permissions.go:31-40`): the self-removal fast path `if u.ID == a.GetID() { return true }` (:36) executes **before** `IsAdmin`. `IsAdmin` (:48-51) is the ONLY place that rejects link shares (`if _, is := a.(*LinkSharing); is { return false }`, :50) — and it is never reached when the fast path returns true. 2. **`BotUser.isOwner`** (`pkg/models/bot_users_permissions.go:47-56`): `return u.BotOwnerID == a.GetID()` (:55), used by `CanRead`/`CanUpdate`/`CanDelete` (:36-45). Unlike `CanCreate` (:27-30) which type-asserts `a.(*user.User)`, these three paths have no principal guard. 3. **`Team.CanRead`** (`pkg/models/teams_permissions.go:68-78`): matches membership on `And("user_id = ?", a.GetID())` (:76) with no link-share guard, unlike sibling `IsAdmin` (:45-49, guard at :47). Link-share JWTs reach these routes: `SetupTokenMiddleware` validates the signature only, `GetAuthFromClaims` returns `*models.LinkSharing`, and the `/user`/`/teams` route groups add no link-share rejection. Link sharing is enabled by default (`config.go` `ServiceEnableLinkSharing.setDefault(true)`). ## Impact A link-share principal (obtainable from any public share link, or self-registered via a share on the attacker's own project) whose id `N` collides with a victim's `users.id == N` can, without being that user or any user: - **Integrity (I:H):** remove the victim from any team they belong to (`DELETE /api/v1/teams/{T}/members/{username}`) → revokes all project permissions the victim inherited through that team. - **Availability/Integrity (A:H, I:H):** enumerate the victim's bot users (`GET /api/v1/user/bots` → `bot_owner_id = a.GetID()`), then disable/rename or **permanently delete** them (`DELETE /api/v1/user/bots/{id}` → `DeleteUser`), destroying data owned solely by those bots. - **Confidentiality (C:H):** read the roster + metadata (name, description, full member list) of any team the colliding user belongs to (`GET /api/v1/teams/{T}`), plus read bot-user records via `isOwner`-gated reads. ## Attack Chain ### Sink 1 — TeamMember.CanDelete (integrity) 1. **Entry:** `POST /api/v1/shares/{hash}/auth` → link-share JWT with `id = N`. **Guard:** JWT middleware — signature only. **Bypass proof:** `GetAuthFromClaims` returns `*models.LinkSharing`; no route-group link-share rejection on the `/teams` group. 2. **Action:** `DELETE /api/v1/teams/{T}/members/{usernameOfUserN}` with the link-share bearer, targeting a team `T` (≥2 members) that user `N` belongs to. **Guard:** `CanDelete` → `GetUserByUsername(tm.Username)` returns user N, then `u.ID == a.GetID()` (`team_members_permissions.go:36`). **Bypass proof:** `a.GetID()` returns `N` (raw positive `share.ID`, `link_sharing.go:84`) == user N's id → `true`. No `a.(*LinkSharing)` check on this branch (only `IsAdmin` at :50 has it, never reached). 3. **Sink:** `Delete` (`team_members.go`) removes user N from team T (last-member check passes when team has ≥2 members). **Impact:** victim loses all project access inherited through team T. ### Sink 2 — BotUser.isOwner (bot takeover / destruction) 1. **Entry:** link-share JWT id N (as above). **Guard:** signature-only; `/user` group adds no link-share reject. 2. **Enumerate:** `GET /api/v1/user/bots` → `ReadAll` runs `Where("bot_owner_id = ?", a.GetID())` = bots owned by user N. **Bypass proof:** `a.GetID()` = N; returns victim's bot ids self-contained (removes the id-guessing barrier). 3. **Sink:** `DELETE /api/v1/user/bots/{botId}` → `CanDelete` → `isOwner` → `u.BotOwnerID == a.GetID()` (`bot_users_permissions.go:55`) → true; `Delete` calls `DeleteUser`. **Bypass proof:** no `a.(*LinkSharing)` guard here (Create-only, :28). **Impact:** disable/rename/permanently delete victim's bot automation identities. ### Sink 3 — Team.CanRead (info disclosure) 1. **Entry:** link-share JWT id N. **Guard:** signature-onl

CWE-639Authorization Bypass Through User-Controlled Key (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #24OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.
Architecture and Design
For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.
Architecture and Design · Implementation
Make sure that the key that is used in the lookup of a specific user's record is not controllable externally by the user or that any tampering can be detected.
Architecture and Design
Use encryption in order to make it more difficult to guess other legitimate values of the key or associate a digital signature with the key so that the server can verify that there has been no tampering.
OWASP Cheat Sheets
Access Control (opens in a new tab)
Authorization Testing Automation (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Insecure Direct Object Reference Prevention (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V4.1.2 (opens in a new tab)
V4.2.1 (opens in a new tab)
V8.3.8 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-843Access of Resource Using Incompatible Type ('Type Confusion') (opens in a new tab)
Base weakness
The product allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.
CWE-863Incorrect Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #17OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-639, CWE-843, CWE-863

Technical details

References

Community reviews

Related threats