CVE-2026-55778Network attack vector

Stored XSS via file-extension blocklist bypass

Published Jul 8, 2026 · Updated Jul 8, 2026

Stored XSS in Parse Server before 8.6.81 and 9.0.0-alpha.1 through 9.9.1-alpha.10 allows remote authenticated users to serve active content. The file-upload validator checks recognized filename extensions against the default blocklist but preserves a dangerous supplied content type when a non-standard or compound extension has no exact blocked match. Exploitation requires file-upload access and an adapter such as S3 or GCS that serves the supplied content type; code runs when another user opens the file URL.

CVSS severity2.1
Low
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Parse Server before 8.6.81 and 9.0.0-alpha.1 through 9.9.1-alpha.10 allows remote authenticated users to serve active content. The file-upload validator checks recognized filename extensions against the default blocklist but preserves a dangerous supplied content type when a non-standard or compound extension has no exact blocked match. Exploitation requires file-upload access and an adapter such as S3 or GCS that serves the supplied content type; code runs when another user opens the file URL.

The record

CVE
CVE-2026-55778
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
Parse Platform
Product
Parse Server
Classifications
CWE-434, T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 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=< 8.6.81
  2. Affected versionversion=>= 9.0.0-alpha.1, < 9.9.1-alpha.11

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Parse Platform · Parse Serverversion=< 8.6.81; version=>= 9.0.0-alpha.1, < 9.9.1-alpha.11

Published CVSS scores

2.1GitHubCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:L/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.

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
T1189Drive-by Compromise

Public exploit references

No public exploit references are available in this record.

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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