CVE-2026-42608Public exploitNetwork attack vector

Unauthenticated file write via unsanitized FormFlash session ID

Published May 11, 2026 · Updated May 11, 2026

Path traversal in Grav FormFlash before 2.0.0-beta.2 allows remote attackers to write attacker-controlled index.yaml files. FormFlash::__construct() appends the raw __form-flash-id session identifier to tmp://forms/ before stream resolution, allowing ../ segments to escape the intended directory. A form-enabled page is required; successful requests create directories and attacker-controlled index.yaml data within paths writable by the web server.

CVSS severity9.1
Critical
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in Grav FormFlash before 2.0.0-beta.2 allows remote attackers to write attacker-controlled index.yaml files. FormFlash::__construct() appends the raw __form-flash-id session identifier to tmp://forms/ before stream resolution, allowing ../ segments to escape the intended directory. A form-enabled page is required; successful requests create directories and attacker-controlled index.yaml data within paths writable by the web server.

The record

CVE
CVE-2026-42608
Published
May 11, 2026
Updated
May 11, 2026
Vendor
Grav
Product
Grav
Classifications
CWE-22, T1190
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=< 2.0.0-beta.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Grav · Gravversion=< 2.0.0-beta.2

Published CVSS scores

8.8GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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.

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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-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1190Exploit Public-Facing Application

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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