CVE-2026-42554Public exploitNetwork attack vector

Cross-site scripting via unescaped AutoFormat HTML branch

Published May 11, 2026 · Updated May 11, 2026

Cross-site scripting in GoFiber Fiber allows remote attackers to execute browser scripts through AutoFormat responses containing attacker-controlled data. DefaultRes.AutoFormat in v3 and Ctx.Format in v2 concatenate a stringified body into a paragraph element without HTML escaping when Accept selects text/html. An application must pass request-influenced data to the formatter, and a victim must render the response in a browser, enabling reflected or stored script execution in that application's origin.

CVSS severity5.3
Medium
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in GoFiber Fiber allows remote attackers to execute browser scripts through AutoFormat responses containing attacker-controlled data. DefaultRes.AutoFormat in v3 and Ctx.Format in v2 concatenate a stringified body into a paragraph element without HTML escaping when Accept selects text/html. An application must pass request-influenced data to the formatter, and a victim must render the response in a browser, enabling reflected or stored script execution in that application's origin.

The record

CVE
CVE-2026-42554
Published
May 11, 2026
Updated
May 11, 2026
Vendor
GoFiber
Product
Fiber
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 11, 2026CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.52.13
  2. Affected versionversion=>= 3.0.0-beta.2, < 3.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

GoFiber · Fiberversion=< 2.52.13; version=>= 3.0.0-beta.2, < 3.1.0

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.3GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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