November 13, 2026 Follow Egret
CVE-2026-119194 · CVE record: PUBLISHED

pyasn1: Quadratic CPU use in schemaless BER/CER/DER container decoding

pyasn1 pyasn1

pyasn1 is a generic ASN.1 library for Python. From 0.3.3 until 0.6.5, schemaless container decoding stores every decoded component's TagSet in a growing set even though only one-versus-multiple tag types must be distinguished. Attacker-controlled BER, CER, or DER input contains many distinct long tag IDs whose TagSet hashes collide. Each later set insertion compares against an increasing number of earlier colliding tags in ConstructedPayloadDecoderBase._decodeComponentsSchemaless, producing quadratic CPU work while decoded values and order remain valid. Repeated inputs can exhaust decoder CPU and reduce service availability. This issue is fixed in version 0.6.5.

Exploitation evidence

Not listed in the latest downloaded CISA KEV catalog. This does not establish an absence of exploitation.

KEV checked 13 Nov 2026, 00:20 Jerusalem · Original catalog ↗

Reported products and versions

pyasn1 / pyasn1

Default status: Not specified

  • affected: >= 0.3.3, < 0.6.5

Fixes and workarounds

No explicit solution text in the downloaded CVE record. Consult the vendor advisory; unaffected version ranges are shown above as reported, not inferred as a patch recommendation.

Sources and related reporting

CVE Program record ↗ · Download tracked evidence as JSON

Monitored source mentions

Shared CVE identifiers link source mentions; they do not establish that the reports describe the same incident.

Observed change timeline

History begins when Egret first downloads each source. It is not the complete upstream CVE history.

12 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-12",
  "epss": 0.00425,
  "percentile": 0.37277
}
10 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-10",
  "epss": 0.00425,
  "percentile": 0.37117
}
09 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-09",
  "epss": 0.00425,
  "percentile": 0.37074
}
08 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-08",
  "epss": 0.00425,
  "percentile": 0.37058
}
07 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-07",
  "epss": 0.00425,
  "percentile": 0.37039
}
06 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-06",
  "epss": 0.00425,
  "percentile": 0.36986
}
06 Nov 2026, 06:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-05",
  "epss": 0.00425,
  "percentile": 0.36964
}
04 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-04",
  "epss": 0.00425,
  "percentile": 0.36946
}
04 Nov 2026, 12:20 Jerusalem · CVE Program record changed

Stored CNA snapshot at this observation.

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-119194",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-11-03T16:23:21.431817Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-11-03T16:23:36.217Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "pyasn1",
          "vendor": "pyasn1",
          "versions": [
            {
              "status": "affected",
              "version": ">= 0.3.3, < 0.6.5"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "pyasn1 is a generic ASN.1 library for Python. From 0.3.3 until 0.6.5, schemaless container decoding stores every decoded component's TagSet in a growing set even though only one-versus-multiple tag types must be distinguished. Attacker-controlled BER, CER, or DER input contains many distinct long tag IDs whose TagSet hashes collide. Each later set insertion compares against an increasing number of earlier colliding tags in ConstructedPayloadDecoderBase._decodeComponentsSchemaless, producing quadratic CPU work while decoded values and order remain valid. Repeated inputs can exhaust decoder CPU and reduce service availability. This issue is fixed in version 0.6.5."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-407",
              "description": "CWE-407: Inefficient Algorithmic Complexity",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-29T19:38:14.056Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p",
          "tags": [
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          ],
          "url": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/pull/132",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/pull/132"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/commit/a36e3a3d067148d26197a6b7221fd0e2cde9cc86",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/commit/a36e3a3d067148d26197a6b7221fd0e2cde9cc86"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.5",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.5"
        }
      ],
      "source": {
        "advisory": "GHSA-fm9c-5rcf-2q5p",
        "discovery": "UNKNOWN"
      },
      "title": "pyasn1: Quadratic CPU use in schemaless BER/CER/DER container decoding"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-119194",
    "datePublished": "2026-10-29T19:38:14.056Z",
    "dateReserved": "2026-10-29T16:04:48.728Z",
    "dateUpdated": "2026-11-03T16:23:36.217Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}
03 Nov 2026, 18:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-03",
  "epss": 0.00425,
  "percentile": 0.36843
}
03 Nov 2026, 06:20 Jerusalem · EPSS observation updated

Stored EPSS snapshot at this observation.

{
  "date": "2026-11-02",
  "epss": 0.00425,
  "percentile": 0.36798
}
03 Nov 2026, 06:20 Jerusalem · CVE Program record changed

Stored CNA snapshot at this observation.

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "pyasn1",
          "vendor": "pyasn1",
          "versions": [
            {
              "status": "affected",
              "version": ">= 0.3.3, < 0.6.5"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "pyasn1 is a generic ASN.1 library for Python. From 0.3.3 until 0.6.5, schemaless container decoding stores every decoded component's TagSet in a growing set even though only one-versus-multiple tag types must be distinguished. Attacker-controlled BER, CER, or DER input contains many distinct long tag IDs whose TagSet hashes collide. Each later set insertion compares against an increasing number of earlier colliding tags in ConstructedPayloadDecoderBase._decodeComponentsSchemaless, producing quadratic CPU work while decoded values and order remain valid. Repeated inputs can exhaust decoder CPU and reduce service availability. This issue is fixed in version 0.6.5."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-407",
              "description": "CWE-407: Inefficient Algorithmic Complexity",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-29T19:38:14.056Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/pull/132",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/pull/132"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/commit/a36e3a3d067148d26197a6b7221fd0e2cde9cc86",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/commit/a36e3a3d067148d26197a6b7221fd0e2cde9cc86"
        },
        {
          "name": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.5",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/pyasn1/pyasn1/releases/tag/v0.6.5"
        }
      ],
      "source": {
        "advisory": "GHSA-fm9c-5rcf-2q5p",
        "discovery": "UNKNOWN"
      },
      "title": "pyasn1: Quadratic CPU use in schemaless BER/CER/DER container decoding"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-119194",
    "datePublished": "2026-10-29T19:38:14.056Z",
    "dateReserved": "2026-10-29T16:04:48.728Z",
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    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}
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