Description
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.
CVSS Metrics
- Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Attack Vector
- network
- Complexity
- low
- Privileges
- none
- User Action
- none
- Scope
- unchanged
- Confidentiality
- none
- Integrity
- none
- Availability
- high
- Weaknesses
- CWE-674
Metadata
- Primary Vendor
- PYASN1
- Published
- 3/18/2026
- Last Modified
- 3/21/2026
- Source
- NIST NVD
- Note: Verify all details with official vendor sources before applying patches.
Affected Products
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