CVE-2026-59884
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk28th percentile - higher than 28% of all known CVEs
Summary
The pyasn1 library before version 0.6.4 has a vulnerability in the BER decoder that does not limit the tag ID size when parsing long-form tags, allowing crafted input to force construction of an arbitrarily large integer with quadratic CPU cost and trigger unhandled ValueError exceptions in Python 3.11+.
Risk Assessment
An attacker can remotely exhaust system resources by sending crafted ASN.1 data, causing excessive CPU usage or application crashes, leading to denial of service (DoS).
Recommendation
Immediately upgrade pyasn1 to version 0.6.4 or later, which includes a fix that limits the tag size.
Other vulnerabilities in pyasn1
See all- CVE-2026-59886High
In pyasn1 prior to 0.6.4, the univ.Real type converts its mantissa, base, and exponent to a Python float using exact big-integer exponentiation. A short BER/CER/DER encoded REAL value can carry a very large exponent, causing excessive CPU and memory consumption and application hangs when prettyPrint(), str(), comparison, arithmetic, int(), or explicit float() is called on untrusted ASN.1 data.
- CVE-2026-59885High
The pyasn1 library before version 0.6.4 has a quadratic time complexity in BER, CER, and DER decoders when processing OBJECT IDENTIFIER and RELATIVE-OID values with many arcs. A small crafted payload with many OID arcs causes excessive CPU consumption per decode() call, potentially leading to denial of service in applications processing untrusted ASN.1 data.
- CVE-2026-30922High
The pyasn1 library prior to version 0.6.3 is vulnerable to a Denial of Service (DoS) attack due to uncontrolled recursion when decoding deeply nested ASN.1 structures. An attacker can craft a payload with thousands of nested SEQUENCE or SET tags with Indefinite Length markers, causing a stack overflow or memory exhaustion.
- CVE-2026-23490High
The pyasn1 library before version 0.6.2 is vulnerable to a Denial-of-Service attack causing memory exhaustion via malformed RELATIVE-OID with excessive continuation octets.
Original NVD description (English source)
pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER codecs parses long-form tags by accumulating continuation octets without an upper bound on the tag ID size, allowing a crafted input to force construction of an arbitrarily large integer with CPU cost growing quadratically and to trigger unhandled ValueError exceptions in Python 3.11+ error formatting paths. Any application decoding untrusted BER, CER, or DER input is affected. This issue is fixed in version 0.6.4.