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Response snapshot Oct 31, 2026, 01:26 UTC

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VulnerabilityCVE-2026-119285

Fiber: CORS wildcard origins matched without a dot boundary, allowing credentialed cross-origin reads

In v2.52.1 and v2.52.2 the CORS middleware matched a wildcard origin such as https://*.example.com by suffix only, without a dot boundary and without comparing the scheme. Any origin whose host ends with the base domain, for example https://evil-example.com or http://notexample.

At a glance

Exploited
Not known
Severity
5.9 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: github.com/gofiber/fiber/v2: 2.52.3. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-g5jq-qmqr-qrwf (opens a new tab)

What happened

Summary

In v2.52.1 and v2.52.2 the CORS middleware matched a wildcard origin such as https://*.example.com by suffix only, without a dot boundary and without comparing the scheme. Any origin whose host ends with the base domain, for example https://evil-example.com or http://notexample.com, was reflected in Access-Control-Allow-Origin, together with Access-Control-Allow-Credentials: true when AllowCredentials is enabled.

v2.52.3 replaced the matcher (#2915) and is not affected. The report was filed against v2.52.15, where the dot boundary holds; see "Other versions" below.

Details

Continue reading

v2.52.1 introduced validateDomain in middleware/cors/utils.go (f0cd3b44, part of the fix for GHSA-fmg4-x8pw-hjhg). It strips scheme and port from both sides and then checks only the suffix, with trimmedPattern = "example.com", so the character before the suffix is never checked:

if strings.HasPrefix(normalizedPattern, "*.") {
 trimmedPattern := normalizedPattern[2:]
 if strings.HasSuffix(normalizedDomain, trimmedPattern) {
 if normalizedDomain != trimmedPattern {
 if strings.TrimSuffix(normalizedDomain, trimmedPattern) != "" {
 return true
 }
 }
 }
}

v2.52.3 (1aac6f61, #2915) replaced it with a scheme-aware prefix/suffix split that keeps the leading dot in the suffix (.example.com).

Proof of concept

app := fiber.New()
app.Use(cors.New(cors.Config{
 AllowOrigins: "https://*.example.com",
 AllowCredentials: true,
}))
app.Get("/", func(c *fiber.Ctx) error { return c.SendString("secret") })

Request with Origin: https://evil-example.com, as a GET and as a preflight (OPTIONS with Access-Control-Request-Method: GET):

| Version | https://evil-example.com | http://evil-example.com | |---|---|---| | v2.52.0 | not allowed | not allowed | | v2.52.1, v2.52.2 | reflected, Access-Control-Allow-Credentials: true | reflected, Access-Control-Allow-Credentials: true | | v2.52.3 to v2.52.16 | not allowed | not allowed |

Impact

An app that configures a wildcard-subdomain AllowOrigins with AllowCredentials: true lets any page on a domain that ends with the base domain (for example notexample.com for *.example.com) read authenticated responses cross-origin. Fixed in v2.52.3; upgrade to the latest v2 release.

Other versions

All v2 releases before v2.52.16 also accepted origins with empty labels (https://.example.com, https://a..example.com), and v2.52.3 to v2.52.15 mis-parsed a wildcard entry after a comma and a space ("https://a.com, https://*.example.com"). No registrable domain produces such an origin, so these are hardening rather than part of this advisory. They are fixed in v2.52.16 (#4792).

Affected package ranges reported by GitHub: github.com/gofiber/fiber/v2: >= 2.52.1, <= 2.52.2

Scores and how they were measured

CVSS base severity

5.9

Version 3.1As of

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-g5jq-qmqr-qrwf (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g5jq-qmqr-qrwf, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 30). Fiber: CORS wildcard origins matched without a dot boundary, allowing credentialed cross-origin reads (CVE-2026-119285). https://kevwire.com/record/CVE-2026-119285

MLA

"Fiber: CORS wildcard origins matched without a dot boundary, allowing credentialed cross-origin reads (CVE-2026-119285)." KEVWire, 30 Oct. 2026, kevwire.com/record/CVE-2026-119285.

Chicago

KEVWire. "Fiber: CORS wildcard origins matched without a dot boundary, allowing credentialed cross-origin reads (CVE-2026-119285)." Last modified October 30, 2026. https://kevwire.com/record/CVE-2026-119285.

Evidence summary (plain text)

Fiber: CORS wildcard origins matched without a dot boundary, allowing credentialed cross-origin reads (Oct 30, 2026).
In v2.52.1 and v2.52.2 the CORS middleware matched a wildcard origin such as https://*.example.com by suffix only, without a dot boundary and without comparing the scheme. Any origin whose host ends with the base domain, for example https://evil-example.com or http://notexample.com, was reflected in Access-Control-Allow-Origin, together with Access-Control-Allow-Credentials: true when AllowCredentials is enabled.

v2.52.3 replaced the matcher (#2915) and is not affected. The report was filed against v2.52.15, where the dot boundary holds; see "Other versions" below.
CVSS 5.9 (version 3.1; evidence as of Oct 30, 2026; https://github.com/advisories/GHSA-g5jq-qmqr-qrwf).
Sources:
GitHub-reviewed advisory GHSA-g5jq-qmqr-qrwf: https://github.com/advisories/GHSA-g5jq-qmqr-qrwf
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-119285.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 31, 2026, 00:50 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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