6.1

CVE-2026-42554: Fiber: XSS in AutoFormat Content Negotiation

Analyzed
AliasesCGA-c84h-q92j-6vm3GHSA-qjv7-627w-8qjvGO-2026-5585
Published 11-05-2026Last modified 15-05-2026

Vulnerability summary

CVE-2026-42554 is a medium (CVSS 6.1) Cross-site Scripting vulnerability in gofiber fiber. EPSS estimates a 0.31% chance of exploitation in the next 30 days, higher than 22.2% of scored vulnerabilities. 1 public exploit is recorded.

Overall risk
34/100
0100
Medium · default modelHow is this calculated?
CVSS score
6.1/10
010
Medium · v3.1 (NVD)
EPSS score
0.31%
0%100%
Low · +0.09 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits1github

Advisory lineage

Upstream 0 · Downstream 3 · Related 4
OPENSUSE-SU-2026:21551-1SUSE-SU-2026:23216-1SUSE-SU-2026:23227-1CGA-7M94-W8FX-6G5V

Timeline

  1. 11-05-2026
    PublishedVulnerability first disclosed.
  2. 15-05-2026
    Last modifiedVulnerability information updated.

Description

Fiber is a web framework for Go. Prior to 2.52.12 and 3.1.0, Cross-Site Scripting vulnerability in Go Fiber allows a remote attacker to inject arbitrary HTML/JavaScript by supplying Accept: text/html on any request whose handler passes attacker-influenced data to the AutoFormat() feature. The developer opts into content negotiation by calling AutoFormat(), but does not opt into raw HTML emission for a particular request; Fiber chooses that branch from attacker-controlled Accept. The html branch is the sole outlier in a method whose name (AutoFormat) and symmetrical structure actively telegraph "safe, format-agnostic reply." This vulnerability is fixed in 2.52.12 and 3.1.0.

CVSS metrics

6 scores · 5 sources · 2 versions

EPSS trend

Probability

0.31%

Chance of exploitation in the next 30 days

Percentile

22%

Versus all other CVEs

30-day change

Increase +0.09 pp

From 0.21% on 22-09-2026

22-09-202622-10-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

1 found
  • githubUnverified

    Fiber

    Maturity: poc

Weaknesses

CWE · root cause

Affected systems

Chainguard4 products
  • gatus< 5.35.0-r11
  • gatus-fips< 5.35.0-r9
  • versitygw< 1.4.1-r2
  • versitygw-fips< 1.4.1-r3
Github.com/gofiber/fiber2 products
  • v2< 2.52.13
  • v3< 3.2.0
Gofiber1 product
  • fiber< 2.52.13 | ≥ 3.0.0-beta.2, < 3.1.0 | < 2.52.12 | ≥ 3.0.0, < 3.1.0
Wolfi1 product
  • gatus< 5.35.0-r11

4 vendors · 8 products

References

4 links