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CVE-2026-30922 — pyasn1 Vulnerable to Denial of Service via Unbounded Recursion

2026-09-29T02:58:14.321993+00:00

Affected: pyasn1, Red Hat Ansible Automation Platform 2.5 for RHEL 8, Red Hat Ansible Automation Platform 2.5 for RHEL 9, Red Hat Ansible Automation Platform 2.6 for RHEL 9, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 10.0 Extended Update Support, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support, Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On, Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support and 33 more

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.

GHSA-jr27-m4p2-rc6r — Denial of Service in pyasn1 via Unbounded Recursion

2026-09-29T02:58:14.322305+00:00

Affected: PyPI: pyasn1

### 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,…

PYSEC-2026-2263

2026-09-29T02:58:14.322395+00:00

Affected: PyPI: pyasn1