CVE-2025-55303Public exploitNetwork attack vector

Cross-site scripting via protocol-relative image URL bypass

Published Aug 19, 2025 · Updated Aug 19, 2025

Cross-site scripting in Astro before 4.16.18 and 5.0.0-alpha.0 through 5.13.1 allows remote attackers to run script via crafted SVG links. The _image endpoint's isRemotePath check treats protocol-relative href values beginning with // as local paths, bypassing configured image domain and remote-pattern allowlists. On-demand rendering must be enabled, and script execution requires a victim to follow an attacker-created same-origin URL that returns a malicious SVG.

CVSS severity6.1
Medium
EPSS probability0.64%
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 Astro before 4.16.18 and 5.0.0-alpha.0 through 5.13.1 allows remote attackers to run script via crafted SVG links. The _image endpoint's isRemotePath check treats protocol-relative href values beginning with // as local paths, bypassing configured image domain and remote-pattern allowlists. On-demand rendering must be enabled, and script execution requires a victim to follow an attacker-created same-origin URL that returns a malicious SVG.

The record

CVE
CVE-2025-55303
Published
Aug 19, 2025
Updated
Aug 19, 2025
Vendor
Astro Technology Company
Product
Astro
Classifications
CWE-79, CWE-115, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 19, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 19, 2025Record 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=< 4.16.18
  2. Affected versionversion=>= 5.0.0-alpha.0, < 5.13.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Astro Technology Company · Astroversion=< 4.16.18; version=>= 5.0.0-alpha.0, < 5.13.2

Published CVSS scores

6.9GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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')
CWE-115Misinterpretation of Input
T1204.001User Execution: Malicious Link

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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