How severe is CVE-2021-41088?

CVE-2021-41088 has a CVSS score of 8.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-41088?

CVE-2021-41088 affects the following packages: github.com/elves/elvish (Go). Ecosystems affected: Go.

How do I fix CVE-2021-41088?

Update github.com/elves/elvish to 0.14.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41088 is resolved across your whole dependency graph.

How do I detect CVE-2021-41088 in my Go dependencies?

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

How do I mitigate CVE-2021-41088 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-2021-41088 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-41088 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-41088?

CVE-2021-41088 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 43th 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-2021-41088?

CVE-2021-41088 is classified as CWE-668 (CWE-668), CWE-346 (CWE-346). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-41088 published, and has it been updated?

CVE-2021-41088 was published on September 23, 2021 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2021-41088 — elvish

HIGHFix: elves/elvish@ccc2750

CVE-2021-41088 is a high-severity (CVSS 8.8) CWE-668 vulnerability in github.com/elves/elvish. A fix is available for github.com/elves/elvish — see the affected versions and patch details below.

Elvish vulnerable to remote code execution via the web UI backend

Also known asGHSA-fpv6-f8jw-rc3rGO-2022-0937

Published

Sep 23, 2021

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk+0.29%

Lower risk than most CVEs43th percentile — riskier than 43% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-41088 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/elves/elvish

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

Description

Impact

Elvish's backend for the experimental web UI (started by elvish -web) hosts an endpoint that allows executing the code sent from the web UI.

The backend does not check the origin of requests correctly. As a result, if the user has the web UI backend open and visits a compromised or malicious website, the website can send arbitrary code to the endpoint in localhost.

Patches

All Elvish releases since 0.14.0 no longer include the experimental web UI, although it is still possible for the user to build a version from source that includes it.

The issue can be patched for previous versions by removing the web UI (found in web, pkg/web or pkg/prog/web, depending on the exact version).

Workarounds

Do not use the experimental web UI.

For more information

If you have any questions or comments about this advisory, please email [email protected].

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/elves/elvish`	all versions	0.14.0`go get github.com/elves/elvish@v0.14.0`

Affected Products

1 product · 1 configurations

Application

elvishelv

< 0.14.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/elves/elvish, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/elves/elvish to 0.14.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41088 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 Elvish's backend for the experimental web UI (started by `elvish -web`) hosts an endpoint that allows executing the code sent from the web UI. The backend does not check the origin of requests correctly. As a result, if the user has the web UI backend open and visits a compromised or malicious website, the website can send arbitrary code to the endpoint in localhost. ### Patches All Elvish releases since 0.14.0 no longer include the experimental web UI, although it is still possible for the user to build a version from source that includes it. The issue can be patched for previ