CVE-2021-31402: The dio package 4.0.0 for Dart allows CRLF injection if the attacker controls the HTTP method string, a differ

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HIGH 7.5REMOTEUPGRADE

CVE-2021-31402 is a high-severity flaw (CVSS 7.5) affecting dio. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.2% (top 33%)
CISA exploited list	No
Weakness	CWE-74
Published	2021-04-15
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: flutterchina

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-04-15 19:15 UTCPublished CVE record published
2026-06-17 03:51 UTCUpdated Record last modified

flutterchina dio UPGRADE

Affected: >= 4.0.0 and < 5.0.0

Fixed in: 5.0.0

Safe to downgrade to: a release before 4.0.0

1. Check installed version

apt-cache policy dio || rpm -q dio || dio --version

2. UPGRADE to 5.0.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade dio

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade dio

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 4.0.0 (Debian / Ubuntu)

apt-cache madison dio sudo apt install dio=<VERSION_BEFORE_4.0.0> sudo apt-mark hold dio

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list dio sudo dnf downgrade dio-<VERSION_BEFORE_4.0.0> sudo dnf versionlock add dio

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-31402?

dio: upgrade to 5.0.0. Exact commands for each OS are on this page.

Is CVE-2021-31402 being exploited?

CVE-2021-31402 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-31402 affect?

CVE-2021-31402 affects dio. Severity is high (CVSS 7.5). 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.

How urgent is CVE-2021-31402?

Priority 53/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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