CVE-2026-41164

nuts-node is the reference implementation of the Nuts specification. Prior to 6.2.3 and 5.4.31, the v1 access token introspection endpoint (/auth/v1/introspect_access_token) accepts any JWT signed by a key present on the node, without validating the JWT type, issuer-to-key binding, or required claims. This allows a Verifiable Presentation (VP) JWT to be replayed as an access token and receive an active: true introspection response. This vulnerability is fixed in 6.2.3 and 5.4.31.

nuts-node is the reference implementation of the Nuts specification. Prior to 6.2.3 and 5.4.31, the v1 access token introspection endpoint (/auth/v1/introspect_access_token) accepts any JWT signed by a key present on the node, without validating the JWT type, issuer-to-key binding, or required claims. This allows a Verifiable Presentation (VP) JWT to be replayed as an access token and receive an active: true introspection response. This vulnerability is fixed in 6.2.3 and 5.4.31.

Summary

The v1 access token introspection endpoint (/auth/v1/introspect_access_token) accepts any JWT signed by a key present on the node, without validating the JWT type, issuer-to-key binding, or required claims. This allows a Verifiable Presentation (VP) JWT to be replayed as an access token and receive an active: true introspection response.

Background

In the v1 auth flow (Nuts RFC003), access tokens are JWTs signed by the authorizer's key with:

• iss = authorizer organization DID
• sub = requester organization DID
• service = purpose of use (e.g. "eOverdracht")
• typ header = "JWT" (default, not explicitly set)

Verifiable Presentations are also JWTs with typ: "JWT" (per W3C VC Data Model 1.1). The W3C VC Data Model 2.0 changed this to vp+jwt specifically to prevent this class of confusion attack (See Securing Verifiable Credentials using JOSE and COSE 3.1.1).

Vulnerability details

The introspection endpoint performs only standard JWT checks. It does not perform the following Nuts-specific access token checks:

1. Validate the typ header: both ATs and VPs use "JWT"
2. Bind iss to the signing key: it doesn't verify that the iss claim matches the DID extracted from the kid
3. Validate required claims: service can be empty; vp claim is silently ignored by FromMap() which uses lenient JSON unmarshaling

Attack scenario

Prerequisites: Attacker (Org B) has received a VP JWT from the victim (Org A) during a normal access token request flow.

1. Org A creates a VP JWT signed with Org A's key and sends it to Org B (normal protocol flow) to request an access token
2. Org B presents this VP JWT to Org A's resource server as a bearer access token
3. Resource server calls Org A's v1 introspection endpoint
4. Introspection checks privateKeyStore.Exists(kid), which passes, because Org A's key is on Org A's node
5. JSON unmarshaling is lenient; the vp claim is silently ignored
6. Returns active: true with service: "", iss: "", sub: <Org A's DID>

Mitigating factors

• service is empty: resource servers that strictly require a non-empty service field may reject the request at the application level
• iss is empty: VP JWTs don't set iss, so resource servers checking this field would see an empty value
• Short-lived VPs: VPs typically expire within minutes, narrowing the attack window
• v1 is legacy: the v2 flow uses opaque access tokens and is not affected

Severity rationale

While the introspection endpoint incorrectly returns active: true for a replayed VP, we consider this not practically exploitable in the current deployment landscape. Resource servers require valid service, iss and aud values to route requests to the correct databases. A replayed VP returns empty service, empty iss, and wrong sub (Org A instead of B), making it unusable for meaningful access. The attack also requires the victim to first present a VP to the attacker through a legitimate protocol flow, and VPs are short-lived.

The severity reflects that the protection against exploitation is accidental (resource servers need service for routing, not for security) and we cannot guarantee how all resource server implementations handle the active: true response with missing fields.

The fix

Affected versions: all v5.x releases prior to v5.4.31, and all v6.x releases prior to v6.2.3. From v5.4.31 and v6.2.3 onward, the following checks have been added to IntrospectAccessToken:

1. iss-to-kid binding: extract the DID from the kid header and verify it matches the iss claim
2. Required claims validation: reject tokens where service is empty
3. typ header validation: requires access tokens to be of typ: "at+jwt"

Additionally, the access token creation code has been updated to use `typ:…

nuts-node is the reference implementation of the Nuts specification. Prior to 6.2.3 and 5.4.31, the v1 access token introspection endpoint (/auth/v1/introspect_access_token) accepts any JWT signed by a key present on the node, without validating the JWT type, issuer-to-key binding, or required claims. This allows a Verifiable Presentation (VP) JWT to be replayed as an access token and receive an active: true introspection response. This vulnerability is fixed in 6.2.3 and 5.4.31.

nuts-node is the reference implementation of the Nuts specification. Prior to 6.2.3 and 5.4.31, the v1 access token introspection endpoint (/auth/v1/introspect_access_token) accepts any JWT signed by a key present on the node, without validating the JWT type, issuer-to-key binding, or required claims. This allows a Verifiable Presentation (VP) JWT to be replayed as an access token and receive an active: true introspection response. This vulnerability is fixed in 6.2.3 and 5.4.31.

Summary

The v1 access token introspection endpoint (/auth/v1/introspect_access_token) accepts any JWT signed by a key present on the node, without validating the JWT type, issuer-to-key binding, or required claims. This allows a Verifiable Presentation (VP) JWT to be replayed as an access token and receive an active: true introspection response.

Background

In the v1 auth flow (Nuts RFC003), access tokens are JWTs signed by the authorizer's key with:

• iss = authorizer organization DID
• sub = requester organization DID
• service = purpose of use (e.g. "eOverdracht")
• typ header = "JWT" (default, not explicitly set)

Verifiable Presentations are also JWTs with typ: "JWT" (per W3C VC Data Model 1.1). The W3C VC Data Model 2.0 changed this to vp+jwt specifically to prevent this class of confusion attack (See Securing Verifiable Credentials using JOSE and COSE 3.1.1).

Vulnerability details

The introspection endpoint performs only standard JWT checks. It does not perform the following Nuts-specific access token checks:

1. Validate the typ header: both ATs and VPs use "JWT"
2. Bind iss to the signing key: it doesn't verify that the iss claim matches the DID extracted from the kid
3. Validate required claims: service can be empty; vp claim is silently ignored by FromMap() which uses lenient JSON unmarshaling

Attack scenario

Prerequisites: Attacker (Org B) has received a VP JWT from the victim (Org A) during a normal access token request flow.

1. Org A creates a VP JWT signed with Org A's key and sends it to Org B (normal protocol flow) to request an access token
2. Org B presents this VP JWT to Org A's resource server as a bearer access token
3. Resource server calls Org A's v1 introspection endpoint
4. Introspection checks privateKeyStore.Exists(kid), which passes, because Org A's key is on Org A's node
5. JSON unmarshaling is lenient; the vp claim is silently ignored
6. Returns active: true with service: "", iss: "", sub: <Org A's DID>

Mitigating factors

• service is empty: resource servers that strictly require a non-empty service field may reject the request at the application level
• iss is empty: VP JWTs don't set iss, so resource servers checking this field would see an empty value
• Short-lived VPs: VPs typically expire within minutes, narrowing the attack window
• v1 is legacy: the v2 flow uses opaque access tokens and is not affected

Severity rationale

While the introspection endpoint incorrectly returns active: true for a replayed VP, we consider this not practically exploitable in the current deployment landscape. Resource servers require valid service, iss and aud values to route requests to the correct databases. A replayed VP returns empty service, empty iss, and wrong sub (Org A instead of B), making it unusable for meaningful access. The attack also requires the victim to first present a VP to the attacker through a legitimate protocol flow, and VPs are short-lived.

The severity reflects that the protection against exploitation is accidental (resource servers need service for routing, not for security) and we cannot guarantee how all resource server implementations handle the active: true response with missing fields.

The fix

Affected versions: all v5.x releases prior to v5.4.31, and all v6.x releases prior to v6.2.3. From v5.4.31 and v6.2.3 onward, the following checks have been added to IntrospectAccessToken:

1. iss-to-kid binding: extract the DID from the kid header and verify it matches the iss claim
2. Required claims validation: reject tokens where service is empty
3. typ header validation: requires access tokens to be of typ: "at+jwt"

Additionally, the access token creation code has been updated to use `typ:…

nuts-node has JWT type confusion in v1 access token introspection that allows VP replay as access token in github.com/nuts-foundation/nuts-node

This update for govulncheck-vulndb fixes the following issues:

• Update to version 0.0.20260723T184607 2026-07-23T18:46:07Z (jsc#PED-11136).

Go CVE Numbering Authority IDs added or updated with aliases:

• GO-2026-4730 CVE-2026-33022 GHSA-cv4x-93xx-wgfj
• GO-2026-4761 CVE-2026-33211 GHSA-j5q5-j9gm-2w5c
• GO-2026-5102 CVE-2026-45021 GHSA-3vcp-chfh-f6r2
• GO-2026-5272 CVE-2026-40938 GHSA-94jr-7pqp-xhcq
• GO-2026-5486 CVE-2026-40924 GHSA-m2cx-gpqf-qf74
• GO-2026-5542 CVE-2026-40090 GHSA-pj97-4p9w-gx3q
• GO-2026-5630 CVE-2026-25542 GHSA-rmx9-2pp3-xhcr
• GO-2026-5643 CVE-2026-40923 GHSA-rx35-6rhx-7858
• GO-2026-5675 CVE-2026-41492 GHSA-vvf7-6rmr-m29q
• GO-2026-5711 CVE-2026-40161 GHSA-wjxp-xrpv-xpff
• GO-2026-5746 CVE-2026-41567 GHSA-x86f-5xw2-fm2r
• GO-2026-5749 CVE-2026-41328 GHSA-x92x-px7w-4gx4
• GO-2026-5837 CVE-2026-44840 GHSA-q2m9-6jp9-c6mc
• GO-2026-5929 CVE-2026-44342 GHSA-26v7-h57m-gh9m
• GO-2026-5930 CVE-2026-33655 GHSA-6qcr-qxgr-m7fv
• GO-2026-5933 GHSA-3g4q-2f67-2gvh
• GO-2026-5934 GHSA-59qp-cfj3-rp64
• GO-2026-5935 GHSA-7856-g3gv-9wq8
• GO-2026-5936 CVE-2026-53552 GHSA-26rh-24rg-j3vv
• GO-2026-5937 CVE-2026-53508 GHSA-2jcc-mxv7-p3f9
• GO-2026-5938 CVE-2026-53553 GHSA-4g5x-hcwm-82jw
• GO-2026-5939 CVE-2026-10517 GHSA-698x-9w2p-7vvp
• GO-2026-5940 CVE-2026-53572 GHSA-6w3m-4hhp-775q
• GO-2026-5941 CVE-2026-53487 GHSA-gvhc-wv3v-7pf8
• GO-2026-5942 CVE-2026-46600
• GO-2026-5944 CVE-2026-50197 GHSA-659f-rgp5-w4wf
• GO-2026-5945 CVE-2026-6815 GHSA-rmxx-v9rj-vpvg
• GO-2026-5946 CVE-2026-52831 GHSA-v5px-423j-pf7p
• GO-2026-5947 CVE-2026-53649 GHSA-xqhv-chqm-fhcc
• GO-2026-5948 CVE-2026-50554 GHSA-588f-fvcv-xhvf
• GO-2026-5949 CVE-2026-50553 GHSA-rqrh-8wpv-x7hh
• GO-2026-5950 CVE-2026-53602 GHSA-339v-266x-79xr
• GO-2026-5951 CVE-2026-10219 GHSA-6jm8-4fhr-5w64
• GO-2026-5952 CVE-2026-49834 GHSA-9vcr-p3rj-q5q6
• GO-2026-5953 CVE-2026-9094 GHSA-c9w5-qp6m-m395
• GO-2026-5956 CVE-2026-55252 GHSA-h5g6-xmh4-hc37
• GO-2026-5957 CVE-2026-54158 GHSA-5xfx-xj4h-5p7r
• GO-2026-5958 CVE-2026-54068 GHSA-gcm7-57gf-953c
• GO-2026-5959 CVE-2026-54072 GHSA-h29v-hj44-q8cv
• GO-2026-5961 CVE-2026-54069 GHSA-hvr9-72v2-fff3
• GO-2026-5962 CVE-2026-54088 GHSA-m93h-4hw7-5qcm
• GO-2026-5963 CVE-2026-54067 GHSA-mvjr-vv3c-w4qv
• GO-2026-5964 CVE-2026-54066 GHSA-p4m3-mgmm-c664
• GO-2026-5965 CVE-2026-54070 GHSA-w7cg-whh7-xp28
• GO-2026-5966 CVE-2026-54089 GHSA-xqp3-jq6g-x3qm
• GO-2026-5967 CVE-2026-50551 GHSA-56mp-4f3v-fgj2
• GO-2026-5968 CVE-2026-54174 GHSA-fpg8-7664-jc5q
• GO-2026-5969 GHSA-g936-7jqj-mwv8
• GO-2026-5970 CVE-2026-56852
• GO-2026-5973 CVE-2026-54250 GHSA-jxr7-mqhw-9p98
• GO-2026-5974 CVE-2026-44300 GHSA-wmj8-9953-vff5
• GO-2026-5975 CVE-2026-50018 GHSA-42j2-w334-qxw7
• GO-2026-5976 CVE-2026-50141 GHSA-g7mm-9vx7-jm7h
• GO-2026-5977 CVE-2026-50013 GHSA-qrh4-p6v4-mrfg
• GO-2026-5978 CVE-2026-50125 GHSA-qw5r-ppcg-f8rj
• GO-2026-5979 CVE-2026-50006 GHSA-xrcf-6jh3-ggvx
• GO-2026-5980 CVE-2026-50158 GHSA-2c7f-fxww-6w6c
• GO-2026-5981 GHSA-mqxv-9rm6-w8qc
• GO-2026-5982 GHSA-pqg7-v6wh-3pfp
• GO-2026-5984 CVE-2026-53604 GHSA-2p2f-px33-4vv5
• GO-2026-5985 GHSA-7rx3-5wx3-5v76
• GO-2026-5986 CVE-2026-61699 GHSA-cm26-5974-52h8
• GO-2026-5987 CVE-2026-55513 GHSA-g4x6-jcvr-9m3g
• GO-2026-5988 CVE-2026-54628 GHSA-hwrq-8wxh-q4xv
• GO-2026-5989 CVE-2026-55512 GHSA-m3cx-mwpg-32jg
• GO-2026-5990 CVE-2026-54629 GHSA-mf78-3rpf-r784
• GO-2026-5991 CVE-2026-53603 GHSA-q4vm-pq3q-8wgq
• GO-2026-5992 CVE-2026-61549 GHSA-qf34-295c-26v8
• GO-2026-5996 CVE-2026-54450 GHSA-pph6-vfjv-vpjw
• GO-2026-5997 CVE-2026-54452 GHSA-xgch-x3mx-cm3c
• GO-2026-5998 CVE-2026-54495 GHSA-398h-7f66-3h4p
• GO-2026-5999 CVE-2026-10814 GHSA-jh6h-v6mp-h22v
• GO-2026-6002 CVE-2026-58196 GHSA-pr64-jmmf-jp54
• GO-2026-6003 CVE-2026-53714 GHSA-22xc-xg2r-9j7v
• GO-2026-6004 CVE-2026-52833 GHSA-3v79-m2cg-89ww
• GO-2026-6005 CVE-2026-53715 GHSA-8fv2-88gg-hm7q
• GO-2026-6006 CVE-2026-53716 GHSA-cxpq-8v7q-cg56 *…