# CVE-2026-26054: SumatraPDF: Heap out-of-bounds read in MOBI header parser.

> A heap out-of-bounds read in SumatraPDF's MOBI parser allows attackers to crash the application by opening a crafted file.

- **Severity:** Medium 6.8 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 24 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** GHSA-27p6-wrfp-pgm8

## What is CVE-2026-26054?

CVE-2026-26054 is a medium-severity memory corruption vulnerability in sumatrapdfreader sumatrapdf, published on 24 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

SumatraPDF is a multi-format reader for Windows. Prior to 3.6, the MobiDoc::ParseHeader function in src/MobiDoc.cpp validates a record using kMobiHeaderMinLen but DecodeMobiDocHeader constructs a decoder sized for kMobiHeaderLen without receiving the actual remaining buffer length. A malformed MOBI file can use an attacker-controlled header length to bypass optional-field early returns and cause the decoder to read beyond a short heap buffer. Opening the crafted document can crash SumatraPDF. This issue is fixed in version 3.6.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-26054?


## How do I fix CVE-2026-26054?

No fix has been published for CVE-2026-26054 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-26054 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-26054 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-26054 and fix it if it is affected.

What it is: CVE-2026-26054 is a medium-severity memory corruption vulnerability in sumatrapdfreader sumatrapdf, published on 24 Sep 2026. It can only be exploited from the same machine or local network, 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-2026-26054 exists.

Affected product: sumatrapdfreader sumatrapdf. 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-2026-26054/ (Markdown: https://insights.sbomify.com/CVE-2026-26054/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-26054
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-26054
- OSV: https://osv.dev/vulnerability/CVE-2026-26054

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-26054/
Summaries are generated and may contain mistakes; the official description above is the record.