CVE-2026-59884CWE-400

pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs

High · published July 14, 2026

CVSS v3.1
7.5
EPSS
1%
Percentile
48.9
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00616 · 48.9th percentile
Weakness
CWE-400 · Uncontrolled Resource Consumption
Published
2026-07-14T16:41Z
EPSS history
Timeline
  • 14 JUL 16:41Z
    pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs
    cvelistv5