How severe is CVE-2026-25891?

No CVSS score has been assigned to CVE-2026-25891 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-25891?

CVE-2026-25891 affects the following packages: github.com/gofiber/fiber/v3 (Go). Ecosystems affected: Go.

How do I fix CVE-2026-25891?

Update github.com/gofiber/fiber/v3 to 3.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25891 is resolved across your whole dependency graph.

How do I detect CVE-2026-25891 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gofiber/fiber/v3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-25891 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-2026-25891?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-25891 can be triaged on real exposure rather than presence alone.

Is CVE-2026-25891 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-25891 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-2026-25891?

CVE-2026-25891 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 48th 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-2026-25891?

CVE-2026-25891 is classified as Path Traversal (CWE-22). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-25891 published, and has it been updated?

CVE-2026-25891 was published on February 24, 2026 and was last updated on August 12, 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

CVE-2026-25891 — v3

Fix: gofiber/fiber@5913370

CVE-2026-25891 is a Path Traversal vulnerability in github.com/gofiber/fiber/v3. A fix is available for github.com/gofiber/fiber/v3 — see the affected versions and patch details below.

Fiber has an Arbitrary File Read in Static Middleware on Windows

Also known asGHSA-m3c2-496v-cw3vGO-2026-4540

Published

Feb 24, 2026

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 21, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-25891.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs48th percentile — riskier than 48% 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.

Real-World Exposure

1 pkg affected

🐹github.com/gofiber/fiber/v3

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

Fiber is an Express inspired web framework written in Go. A Path Traversal (CWE-22) vulnerability in Fiber allows a remote attacker to bypass the static middleware sanitizer and read arbitrary files on the server file system on Windows. This affects Fiber v3 through version 3.0.0. This has been patched in Fiber v3 version 3.1.0.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/gofiber/fiber/v3`	all versions	3.1.0`go get github.com/gofiber/fiber/v3@v3.1.0`

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/gofiber/fiber/v3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/gofiber/fiber/v3 to 3.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25891 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-25891 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-25891. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2026-25891 in your dependencies?

O3 Security finds CVE-2026-25891 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works