CVE-2026-59885: pyasn1 Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-8ppf-4f7h-5ppj
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CVSS 7.5
CWE-400 CWE-407
Published
Advisory Summary

CVE-2026-59885 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting pyasn1 libraries in the PyPI ecosystem. The issue involves quadratic complexity in object identifier and relative-oid processing allows denial of service. Remediation is available by upgrading affected packages to version 0.6.4.

CVE-2026-59885 at a Glance

CVE Identifier CVE-2026-59885
GHSA Identifier GHSA-8ppf-4f7h-5ppj
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product pyasn1
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-59885

To remediate this vulnerability, upgrade all affected pyasn1 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

pyasn1 fixed: 0.6.4 
pip install pyasn1>=0.6.4
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show pyasn1

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-59885, inspect your installed packages using pip:

pip show pyasn1

Analyze the terminal output to locate any version of pyasn1 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.6.4), your application is affected.

Note: The pip show pyasn1 command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In pyasn1, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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.

CVE-2026-59885 Affected pyasn1 Versions

1 component(s)
Fixed Versions:
0.6.4
Product / Package Ecosystem Affected Versions Fixed Version
pyasn1
pypi/pyasn1
PyPI
< 0.6.4
0.6.4

References

GitHub Advisory / Wiki ADVISORY
https://github.com/pyasn1/pyasn1/security/advisories/GHSA-8ppf-4f7h-5ppj
NVD — CVE-2026-59885 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59885
Security Fix Commit FIX COMMIT
https://github.com/pyasn1/pyasn1/commit/45bdb19eb7df4b3780fe9c912c63e99bffc39dd9
pyasn1 Source Repository REPOSITORY
https://github.com/pyasn1/pyasn1
pyasn1 Release RELEASE
https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4

Frequently Asked Questions

What is CVE-2026-59885?
CVE-2026-59885 is a security vulnerability in pyasn1 involving Quadratic complexity in OBJECT IDENTIFIER and RELATIVE-OID processing allows denial of service under CWE-400: Uncontrolled Resource Consumption.
Which pyasn1 versions are affected?
Affected versions include releases prior to 0.6.4 across affected packages: pyasn1.
What version fixes CVE-2026-59885?
Upgrading to 0.6.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pyasn1 affected?
Yes, pyasn1 is affected in releases prior to 0.6.4. Upgrade your dependency to 0.6.4 or later.
What is the CVSS score of CVE-2026-59885?
CVE-2026-59885 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-59885?
CVE-2026-59885 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check PyPI dependencies for CVE-2026-59885?
Run the dependency tree command: 'pip show pyasn1'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8ppf-4f7h-5ppj",
  "modified" : "2026-07-21T19:11:03Z",
  "published" : "2026-07-21T19:11:03Z",
  "aliases" : [ "CVE-2026-59885" ],
  "summary" : "pyasn1: Quadratic complexity in OBJECT IDENTIFIER and RELATIVE-OID processing allows denial of service",
  "details" : "### Impact\nThe 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.\n\nThe 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.\n\n### Affected components\nObjectIdentifierPayloadDecoder 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.\n\n### Patches\nFixed in pyasn1 0.6.4: arc accumulation in both decoders and encoders now runs in linear time.\n\n### Workarounds\nLimit the size of untrusted ASN.1 input before decoding.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pyasn1"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.6.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.6.3"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-8ppf-4f7h-5ppj"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-59885"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pyasn1/pyasn1/commit/45bdb19eb7df4b3780fe9c912c63e99bffc39dd9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/pyasn1/pyasn1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-407" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-21T19:11:03Z",
    "nvd_published_at" : "2026-07-14T17:17:14Z"
  }
}