How severe is CVE-2021-33564?

CVE-2021-33564 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-33564?

CVE-2021-33564 affects the following packages: dragonfly (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2021-33564?

Update dragonfly to 1.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33564 is resolved across your whole dependency graph.

How do I detect CVE-2021-33564 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dragonfly, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-33564 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2021-33564?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-33564 can be triaged on real exposure rather than presence alone.

Is CVE-2021-33564 actively exploited in the wild?

Yes. There are 7 known exploit references for CVE-2021-33564, including 6 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-33564?

CVE-2021-33564 has an EPSS (Exploit Prediction Scoring System) score of 72.1%, placing it in the 99th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-33564?

CVE-2021-33564 is classified as CWE-88 (CWE-88). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2021-33564?

A Nuclei detection template exists for CVE-2021-33564, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-33564 published, and has it been updated?

CVE-2021-33564 was published on May 29, 2021 and was last updated on July 8, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎

💎 RubyGems

Not in CISA KEV

CRITICAL severity

CVE-2021-33564 — dragonfly

CRITICALFix: markevans/dragonfly@2539929

CVE-2021-33564 is a critical-severity (CVSS 9.8) CWE-88 vulnerability in dragonfly. 7 public exploit references exist, so weaponization risk is real. A fix is available for dragonfly — see the affected versions and patch details below.

Dragonfly contains remote code execution vulnerability

Also known asGHSA-j858-xp5v-f8xx

Published

May 29, 2021

Updated

Jul 8, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

7 known

Exploitation data as of Sep 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

72.1%probability of exploitation in next 30 days

Very High Risk0.00%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

How urgent is this, really

CVE-2021-33564 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.

Where this sits among everything scored

Of 378,156 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.

Real-World Exposure

1 pkg affected

💎dragonfly

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

An argument injection vulnerability in the Dragonfly gem before 1.4.0 for Ruby allows remote attackers to read and write to arbitrary files via a crafted URL when the verify_url option is disabled. This may lead to code execution. The problem occurs because the generate and process features mishandle use of the ImageMagick convert utility.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`dragonfly`	all versions	1.4.0`bundle update dragonfly --conservative`

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.