CVE-2026-54334Network attack vector

Process crash via unchecked ReadCLen array writes

Published Sep 14, 2026 · Updated Sep 14, 2026

Heap out-of-bounds write in UEFI Firmware Parser 1.13 and earlier allows attackers to crash the parsing process via crafted firmware. ReadCLen reads a 9-bit count of up to 511 into the 510-element mCLen heap array, while its run-length branch issues up to 531 zero writes without enforcing the array bound. Processing a crafted Tiano or EFI compressed section is required; the established consequence is a deterministic process crash, while code execution depends on build and runtime details.

CVSS severity9.8
Critical
EPSS probability0.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap out-of-bounds write in UEFI Firmware Parser 1.13 and earlier allows attackers to crash the parsing process via crafted firmware. ReadCLen reads a 9-bit count of up to 511 into the 510-element mCLen heap array, while its run-length branch issues up to 531 zero writes without enforcing the array bound. Processing a crafted Tiano or EFI compressed section is required; the established consequence is a deterministic process crash, while code execution depends on build and runtime details.

The record

CVE
CVE-2026-54334
Published
Sep 14, 2026
Updated
Sep 14, 2026
Vendor
Theopolis
Product
UEFI Firmware Parser
Classifications
CWE-787
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 14, 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=< 1.14

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Theopolis · UEFI Firmware Parserversion=< 1.14

Published CVSS scores

9.8TheopolisCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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