# CVE-2026-48104: GHSL-2026-120: 7-Zip SquashFS BlockToNode uninitialized heap read

> Attackers can cause denial of service or disclose heap memory by tricking users into opening a crafted SquashFS archive in 7-Zip.

- **Severity:** Medium 4.2 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 5 Jun 2026
- **Updated:** 5 Jun 2026
- **Also known as:** ALPINE-CVE-2026-48104, DEBIAN-CVE-2026-48104, ECHO-f5e5-f521-ddd7, MINI-p88c-h56p-q7r5, UBUNTU-CVE-2026-48104

## What is CVE-2026-48104?

CVE-2026-48104 is a medium-severity vulnerability in mcmilk 7-Zip, published on 5 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

7-Zip is a file archiver with a high compression ratio. Versions 9.18 through 26.00 contain an uninitialized heap read in the SquashFS archive handler caused by a sparsely populated index array. In the SquashFS handler, _blockToNode is allocated with capacity for every metadata block but populated only when an inode crosses a block boundary, so a crafted image with few inodes spanning many blocks leaves most slots holding raw heap contents (the underlying allocator does not zero-initialize POD storage). When OpenDir looks up an attacker-influenced blockIndex (derived from the RootInode superblock field), it reads two of these uninitialized slots and passes them as the left/right bounds of a binary search over _nodesPos, which dereferences the midpoint without bounds checking; if the resulting value happens to match the search key, the returned index is used to read a full node struct from _nodes whose fields feed further directory parsing, forming a chained OOB read primitive that is heap-layout-dependent and not reliably triggerable. The SquashFS handler is enabled by default in stock 7z.dll and the issue triggers during Open() with no interaction beyond opening the file; impact is denial of service from wild-pointer dereference and potential heap information disclosure, with no write primitive. Version 26.01 fixes the issue.

Weakness: CWE-908 (Use of Uninitialized Resource), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-48104?

It affects 1 product.


Products: 7-Zip 7-Zip.

## How do I fix CVE-2026-48104?

Upgrade to a fixed version.

## Is CVE-2026-48104 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48104 exists.

## Other vulnerabilities in mcmilk 7-Zip

- [CVE-2025-0411](https://insights.sbomify.com/CVE-2025-0411/): 7-Zip Mark of the Web Bypass (high 7.0, exploited in the wild)
- [CVE-2008-6536](https://insights.sbomify.com/CVE-2008-6536/): Other in n/a (critical 10.0)
- [CVE-2026-48095](https://insights.sbomify.com/CVE-2026-48095/): GHSL-2026-140_7-Zip: 7-Zip has a heap buffer overflow via NTFS compressed stream buffer under-allocation (high 8.8)
- [CVE-2018-10172](https://insights.sbomify.com/CVE-2018-10172/): Privilege escalation in n/a (high 8.8)
- [CVE-2016-2335](https://insights.sbomify.com/CVE-2016-2335/): Memory corruption in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-48104 and fix it if it is affected.

What it is: CVE-2026-48104 is a medium-severity vulnerability in mcmilk 7-Zip, published on 5 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48104 exists.

Affected product: mcmilk 7-Zip. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-48104/ (Markdown: https://insights.sbomify.com/CVE-2026-48104/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48104
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48104
- OSV: https://osv.dev/vulnerability/CVE-2026-48104

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-48104/
Summaries are generated and may contain mistakes; the official description above is the record.