How severe is CVE-2021-31402?

CVE-2021-31402 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-31402?

CVE-2021-31402 affects the following packages: dio (Pub). Ecosystems affected: Pub.

How do I fix CVE-2021-31402?

Update dio to 5.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-31402 is resolved across your whole dependency graph.

How do I detect CVE-2021-31402 in my Pub dependencies?

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

How do I mitigate CVE-2021-31402 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.

Is CVE-2021-31402 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-31402, including 1 in-the-wild exploitation 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-2021-31402?

CVE-2021-31402 has an EPSS (Exploit Prediction Scoring System) score of 1.2%, placing it in the 68th 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. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-31402?

CVE-2021-31402 is classified as CWE-74 (CWE-74). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-31402 published, and has it been updated?

CVE-2021-31402 was published on April 15, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🎯

🎯 Pub

Not in CISA KEV

HIGH severity

CVE-2021-31402 — dio

HIGHFix: cfug/dio@927f79e

CVE-2021-31402 is a high-severity (CVSS 7.5) CWE-74 vulnerability in dio. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for dio — see the affected versions and patch details below.

dio vulnerable to CRLF injection with HTTP method string

Also known asGHSA-9324-jv53-9cc8

Published

Apr 15, 2021

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🎯dio

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

Description

Impact

The dio package 4.0.0 for Dart allows CRLF injection if the attacker controls the HTTP method string, a different vulnerability than CVE-2020-35669.

Patches

The vulnerability has been resolved by https://github.com/cfug/dio/commit/927f79e93ba39f3c3a12c190624a55653d577984, and included since v5.0.0.

Workarounds

Cherry-pick the commit to your own fork can resolves the vulberability too.

References

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🎯Pub	`dio`	all versions	5.0.0`dart pub upgrade dio`

Affected Products

1 product · 1 configurations

Application

dioflutterchina

≥ 4.0.0 && < 5.0.0

range

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.

The dio package 4.0.0 for Dart allows CRLF injection if the attacker con…

github.comNVDApr 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dio, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update dio to 5.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-31402 is resolved across your whole dependency graph.
Workarounds
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.

Frequently Asked Questions

### Impact The dio package 4.0.0 for Dart allows CRLF injection if the attacker controls the HTTP method string, a different vulnerability than CVE-2020-35669. ### Patches The vulnerability has been resolved by https://github.com/cfug/dio/commit/927f79e93ba39f3c3a12c190624a55653d577984, and included since v5.0.0. ### Workarounds Cherry-pick the commit to your own fork can resolves the vulberability too. ### References - https://nvd.nist.gov/vuln/detail/CVE-2021-31402 - https://osv.dev/GHSA-jwpw-q68h-r678 - https://github.com/cfug/dio/issues/1130 - https://github.com/cfug/dio/issues/1752