CVE-2026-48101: CWE-908: Use of Uninitialized Resource in mcmilk 7-Zip
7-Zip is a file archiver with a high compression ratio. Versions 9.21 through 26.00 contain an An uninitialized memory disclosure vulnerability in the UEFI capsule (.scap) parser in 7-Zip. The OpenCapsule function allocates a heap buffer of attacker-declared CapsuleImageSize (up to 1 GiB) without zero-initialization, then reads the file contents into it with ReadStream_FALSE whose return value is silently discarded. If the file is truncated, the unread tail of the buffer retains uninitialized heap memory, which is then exposed as extracted file content via GetStream. Version 26.0.1 fixes the issue.
AI Analysis
Technical Summary
CVE-2026-48101 is a use of uninitialized resource vulnerability (CWE-908) in the mcmilk 7-Zip file archiver. Specifically, the UEFI capsule (.scap) parser's OpenCapsule function allocates a heap buffer sized by an attacker-controlled CapsuleImageSize without zeroing it. The function reads file contents into this buffer using ReadStream_FALSE but ignores the return value. If the input file is truncated, the unread portion of the buffer contains uninitialized heap memory, which can then be exposed through the GetStream function as extracted file content. This affects 7-Zip versions from 9.21 up to but not including 26.01. Version 26.0.1 addresses this issue.
Potential Impact
The vulnerability can lead to disclosure of uninitialized heap memory contents when extracting specially crafted truncated UEFI capsule files. This may expose sensitive information from the process memory space. The CVSS 3.1 base score is 6.5 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, user interaction required, and high confidentiality impact with no integrity or availability impact.
Mitigation Recommendations
Version 26.0.1 of 7-Zip fixes this vulnerability by properly handling buffer initialization and read operations in the UEFI capsule parser. Users should upgrade to 7-Zip 26.0.1 or later to remediate this issue. Patch status is not explicitly confirmed in the vendor advisory, but the description states version 26.0.1 fixes the issue. No other mitigations are indicated.
CVE-2026-48101: CWE-908: Use of Uninitialized Resource in mcmilk 7-Zip
Description
7-Zip is a file archiver with a high compression ratio. Versions 9.21 through 26.00 contain an An uninitialized memory disclosure vulnerability in the UEFI capsule (.scap) parser in 7-Zip. The OpenCapsule function allocates a heap buffer of attacker-declared CapsuleImageSize (up to 1 GiB) without zero-initialization, then reads the file contents into it with ReadStream_FALSE whose return value is silently discarded. If the file is truncated, the unread tail of the buffer retains uninitialized heap memory, which is then exposed as extracted file content via GetStream. Version 26.0.1 fixes the issue.
CVSS v3.1
Score 6.5medium
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-48101 is a use of uninitialized resource vulnerability (CWE-908) in the mcmilk 7-Zip file archiver. Specifically, the UEFI capsule (.scap) parser's OpenCapsule function allocates a heap buffer sized by an attacker-controlled CapsuleImageSize without zeroing it. The function reads file contents into this buffer using ReadStream_FALSE but ignores the return value. If the input file is truncated, the unread portion of the buffer contains uninitialized heap memory, which can then be exposed through the GetStream function as extracted file content. This affects 7-Zip versions from 9.21 up to but not including 26.01. Version 26.0.1 addresses this issue.
Potential Impact
The vulnerability can lead to disclosure of uninitialized heap memory contents when extracting specially crafted truncated UEFI capsule files. This may expose sensitive information from the process memory space. The CVSS 3.1 base score is 6.5 (medium severity), reflecting network attack vector, low attack complexity, no privileges required, user interaction required, and high confidentiality impact with no integrity or availability impact.
Mitigation Recommendations
Version 26.0.1 of 7-Zip fixes this vulnerability by properly handling buffer initialization and read operations in the UEFI capsule parser. Users should upgrade to 7-Zip 26.0.1 or later to remediate this issue. Patch status is not explicitly confirmed in the vendor advisory, but the description states version 26.0.1 fixes the issue. No other mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-20T18:40:45.835Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a22efd8e29bf47b50886a20
Added to database: 06/05/2026, 15:48:40 UTC
Last enriched: 06/05/2026, 16:03:41 UTC
Last updated: 07/31/2026, 19:22:59 UTC
Views: 251
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