github.com/go-viper/mapstructure/v2 · Vulnerability

A flaw was found in github.com/go-viper/mapstructure/v2, in the field processing component using mapstructure.WeakDecode. This vulnerability allows information disclosure through detailed error messages that may leak sensitive input values via malformed user-supplied data processed in security-critical contexts.

A flaw was found in github.com/go-viper/mapstructure/v2, in the field processing component using mapstructure.WeakDecode. This vulnerability allows information disclosure through detailed error messages that may leak sensitive input values via malformed user-supplied data processed in security-critical contexts.

A flaw was found in github.com/go-viper/mapstructure/v2, in the field processing component using mapstructure.WeakDecode. This vulnerability allows information disclosure through detailed error messages that may leak sensitive input values via malformed user-supplied data processed in security-critical contexts.

### Summary Use of this library in a security-critical context may result in leaking sensitive information, if used to process sensitive fields. ### Details OpenBao (and presumably HashiCorp Vault) have surfaced error messages from `mapstructure` as follows: https://github.com/openbao/openbao/blob/98c3a59c040efca724353ca46ca79bd5cdbab920/sdk/framework/field_data.go#L43-L50 ```go _, _, err := d.getPrimitive(field, schema) if err != nil { return fmt.Errorf("error converting input for field %q: %w", field, err) } ``` where this calls `mapstructure.WeakDecode(...)`: https://github.com/openbao/openbao/blob/98c3a59c040efca724353ca46ca79bd5cdbab920/sdk/framework/field_data.go#L181-L193 ```go func (d *FieldData) getPrimitive(k string, schema *FieldSchema) (interface{}, bool, error) { raw, ok := d.Raw[k] if !ok { return nil, false, nil } switch t := schema.Type; t { case TypeBool: var result bool if err := mapstructure.WeakDecode(raw, &result); err != nil { return nil, false, err } return result, true, nil ``` Notably, `WeakDecode(...)` eventually calls one of the decode helpers, which surfaces the original value via `strconv` helpers: https://github.com/go-viper/mapstructure/blob/8c61ec1924fcfa522f9fc6b4618c672db61d1a38/mapstructure.go#L720-L727 https://github.com/go-viper/mapstructure/blob/8c61ec1924fcfa522f9fc6b4618c672db61d1a38/mapstructure.go#L791-L798 https://github.com/go-viper/mapstructure/blob/8c61ec1924fcfa522f9fc6b4618c672db61d1a38/decode_hooks.go#L180 & more. These are different code paths than are fixed in the previous iteration at https://github.com/go-viper/mapstructure/security/advisories/GHSA-fv92-fjc5-jj9h. ### PoC To reproduce with OpenBao: ``` $ podman run --pull=always -p 8300:8300 openbao/openbao:latest server -dev -dev-root-token-id=root -dev-listen-address=0.0.0.0:8300 ``` and in a new tab: ``` $ BAO_TOKEN=root BAO_ADDR=http://localhost:8300 bao auth enable userpass Success! Enabled userpass auth method at: userpass/ $ curl -X PUT -H "X-Vault-Request: true" -H "X-Vault-Token: root" -d '{"ttl":"asdf"}' "http://localhost:8200/v1/auth/userpass/users/asdf" --> server logs: 2025-06-25T21:32:25.101-0500 [ERROR] core: failed to run existence check: error="error converting input for field \"ttl\": time: invalid duration \"asdf\"" ``` ### Impact This is an information disclosure bug with little mitigation. See https://discuss.hashicorp.com/t/hcsec-2025-09-vault-may-expose-sensitive-information-in-error-logs-when-processing-malformed-data-with-the-kv-v2-plugin/74717 for a previous version. That version was fixed, but this is in the second part of that error message (starting at `'' expected a map, got 'string'` -- when the field type is `string` and a `map` is provided, we see the above information leak -- the previous example had a `map` type field with a `string` value provided). This was rated 4.5 Medium by HashiCorp in the past iteration.

Go-viper's mapstructure May Leak Sensitive Information in Logs in github.com/go-viper/mapstructure