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Critical

Security advisory

Type: advisorySources: OSVCVE: CVE-2021-33026

The Flask-Caching extension through 1.10.1 for Flask relies on Pickle for serialization, which may lead to remote code execution or local privilege escalation. If an attacker gains access to cache storage (e.g., filesystem, Memcached, Redis, etc.), they can construct a crafted payload, poison the cache, and execute Python code. NOTE: a third party indicates that exploitation is extremely unlikely unless the machine is already compromised; in other cases, the attacker would be unable to write their payload to the cache and generate the required collision

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2021-33026
Confirmed fixed CVEs
Not specified
Updated in this feed
31 Oct 2026, 11:18 UTC · Revision 1

Source evidence

CVE-2021-33026

core-osv · Original source

Published 13 May 2021, 23:15 UTC

The Flask-Caching extension through 1.10.1 for Flask relies on Pickle for serialization, which may lead to remote code execution or local privilege escalation. If an attacker gains access to cache storage (e.g., filesystem, Memcached, Redis, etc.), they can construct a crafted payload, poison the cache, and execute Python code. NOTE: a third party indicates that exploitation is extremely unlikely unless the machine is already compromised; in other cases, the attacker would be unable to write their payload to the cache and generate the required collision

osv:CVE-2021-33026
Complete source record
{
  "id": "ca661220fef53a03f3d56a2f8fd1fae69900119acd912b4fb794e23355793210",
  "url": "https://osv.dev/vulnerability/CVE-2021-33026",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "CVE-2021-33026",
    "summary": "The Flask-Caching extension through 1.10.1 for Flask relies on Pickle for serialization, which may lead to remote code execution or local privilege escalation. If an attacker gains access to cache storage (e.g., filesystem, Memcached, Redis, etc.), they can construct a crafted payload, poison the cache, and execute Python code. NOTE: a third party indicates that exploitation is extremely unlikely unless the machine is already compromised; in other cases, the attacker would be unable to write their payload to the cache and generate the required collision",
    "evidence": "osv:CVE-2021-33026",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2021-33026",
      "aliases": [
        "CVE-2021-33026",
        "GHSA-656c-6cxf-hvcv"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/pallets-eco/flask-caching",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "last_affected": "31f6949c499dc8b57ce1db04c1841105d4631eb1"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:flask-caching_project:flask-caching:*:*:*:*:*:flask:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "1.10.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.10.1",
            "v1.10.0",
            "v1.9.0",
            "v1.8.0",
            "v1.7.2",
            "v1.7.1",
            "v1.7.0",
            "v1.6.0",
            "v1.5.0",
            "v1.4.0",
            "v1.3.3",
            "v1.3.2",
            "v1.3.1",
            "v1.3.0",
            "1.0.0",
            "R-0.11",
            "R-0.8",
            "R-1.7.1",
            "R-0.7",
            "R-0.6",
            "R-0.4",
            "R-0.3.3",
            "R-0.3.2",
            "R-0.3.1",
            "R-0.3"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-33026.json"
          }
        }
      ],
      "modified": "2026-10-20T10:53:47.365806041Z",
      "provider": "osv",
      "references": [
        "https://github.com/pallets-eco/flask-caching/pull/209#issuecomment-1136397937",
        "https://github.com/sh4nks/flask-caching/pull/209"
      ],
      "provider_metadata": {}
    },
    "related_cves": [
      {
        "value": "CVE-2021-33026",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 384633,
  "published_at": "2021-05-13T23:15:07.367+00:00"
}