CVE-2021-4235: Due to unbounded alias chasing, a maliciously crafted YAML file can cause the system to consume significant sy

Q: How do I fix CVE-2021-4235?

yaml: upgrade to 2.2.3. Exact commands for each OS are on this page.

Q: Is CVE-2021-4235 being exploited?

CVE-2021-4235 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-4235 affect?

CVE-2021-4235 affects yaml. Severity is medium (CVSS 5.5). Due to unbounded alias chasing, a maliciously crafted YAML file can cause the system to consume significant system resources. If parsing user input, this may be used as a denial of service vector.

Q: How urgent is CVE-2021-4235?

Priority 33/100. Public exploit reference

Routine

MEDIUM 5.5UPGRADE

CVE-2021-4235 is a medium-severity flaw (CVSS 5.5) affecting yaml. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Due to unbounded alias chasing, a maliciously crafted YAML file can cause the system to consume significant system resources. If parsing user input, this may be used as a denial of service vector.

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.4% (top 63%)
CISA exploited list	No
Published	2022-12-27
Last modified	2026-06-17

Publisher (CNA): Go Project · Vendor: yaml project

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

Am I affected?

Timeline

2022-12-27 22:15 UTCPublished CVE record published
2026-06-17 04:19 UTCUpdated Record last modified

yaml project yaml UPGRADE

Affected: < 2.2.3

Fixed in: 2.2.3

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 2.2.3 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade yaml

Note

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

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-2021-4235?

yaml: upgrade to 2.2.3. Exact commands for each OS are on this page.

Is CVE-2021-4235 being exploited?

CVE-2021-4235 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-2021-4235 affect?

CVE-2021-4235 affects yaml. Severity is medium (CVSS 5.5). Due to unbounded alias chasing, a maliciously crafted YAML file can cause the system to consume significant system resources. If parsing user input, this may be used as a denial of service vector.

How urgent is CVE-2021-4235?

Priority 33/100. Public exploit reference

Related CVEs

CVE-2026-33532 MEDIUM 4.3 UPGRADE `yaml` is a YAML parser and serialiser for JavaScript
CVE-2023-2251 HIGH 7.5 UPGRADE Uncaught Exception in GitHub repository eemeli/yaml prior to 2.0.0-5.
CVE-2022-3064 HIGH 7.5 UPGRADE Parsing malicious or large YAML documents can consume excessive amounts of CPU or memory.
CVE-2022-28948 HIGH 7.5 DOWNGRADE MITIGATE An issue in the Unmarshal function in Go-Yaml v3 causes the program to crash when attempting to deserialize in

References

← Back to latest CVEs