GHSA-8ppf-4f7h-5ppj CVE-2026-59885 PYSEC-2026-3456
pyasn1: Quadratic complexity in OBJECT IDENTIFIER and RELATIVE-OID processing allows denial of service
- Severity
- 7.5 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.62%
- Chance of exploitation in the next 30 days. Higher than 49.54% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
0.6.4- Upgrade pyasn1 to this version or later
Description
Impact
The BER/CER/DER decoders process OBJECT IDENTIFIER and RELATIVE-OID values in quadratic time relative to the number of arcs. A small crafted payload (tens of kilobytes) containing an OID with many arcs consumes seconds of CPU per decode() call, allowing denial of service in any application that decodes untrusted ASN.1 data (certificates, LDAP, SNMP, Kerberos, etc.). The corresponding encoders have the same quadratic behavior, reachable when an application re-encodes previously decoded attacker-supplied values.
The arc-size limit introduced for CVE-2026-23490 bounds the byte length of an individual arc but not the number of arcs, so it does not mitigate this issue.
Affected components
ObjectIdentifierPayloadDecoder and RelativeOIDPayloadDecoder in pyasn1/codec/ber/decoder.py; ObjectIdentifierEncoder and RelativeOIDEncoder in pyasn1/codec/ber/encoder.py. The CER and DER codecs inherit these and are equally affected.
Patches
Fixed in pyasn1 0.6.4: arc accumulation in both decoders and encoders now runs in linear time.
Workarounds
Limit the size of untrusted ASN.1 input before decoding.
Affected versions
PyPI
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
pyasn1 PyPI → 0.6.4
- pip
pip install --upgrade "pyasn1>=0.6.4"- poetry
poetry add "pyasn1>=0.6.4"- uv
uv add "pyasn1>=0.6.4"
Severity breakdown
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Weakness
CWE-400: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How to prevent it
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Implementation: Ensure that all failures in resource allocation place the system into a safe posture.
CWE-407: Inefficient Algorithmic Complexity
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-2qm8-x737-gmw5 pyasn1 has quadratic CPU consumption in constructed BIT STRING decoding | High | Also affects pyasn1 |
| GHSA-mm57-4v3p-rchx pyasn1 has quadratic-complexity denial of service in binary REAL decoding | High | Also affects pyasn1 |
| GHSA-9m75-vc3g-4x39 pyasn1 has quadratic-time denial of service in constructed string and indefinite-length ANY decoding | High | Also affects pyasn1 |
| GHSA-fm9c-5rcf-2q5p pyasn1 has quadratic CPU use in schemaless BER/CER/DER container decoding | High | Also affects pyasn1 |
| GHSA-hm4w-wwcw-mr6r pyasn1: Uncontrolled resource consumption when converting decoded REAL values | High | Also affects pyasn1 |
| GHSA-m4p7-r5rc-7g4j pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs | High | Also affects pyasn1 |
| GHSA-jr27-m4p2-rc6r Denial of Service in pyasn1 via Unbounded Recursion | High | Also affects pyasn1 |
| GHSA-63vm-454h-vhhq pyasn1 has a DoS vulnerability in decoder | High | Also affects pyasn1 |
Credits: tynus2
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