# CVE-2026-71391: Off-by-One Error in GNU Emacs for Android

> A crafted TrueType font triggers an off-by-one error in GNU Emacs for Android, allowing heap memory disclosure to defeat ASLR.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N`)
- **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:** No
- **Published:** 10 Aug 2026
- **Updated:** 10 Aug 2026
- **Also known as:** GHSA-49vj-r7f8-c3p6, UBUNTU-CVE-2026-71391

## What is CVE-2026-71391?

CVE-2026-71391 is a medium-severity memory corruption vulnerability in GNU Emacs, published on 10 Aug 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

GNU Emacs for Android contains an off-by-one error in the gvar table parser in src/sfnt.c. The shared-coordinate index boundary check in sfnt_vary_simple_glyph() and sfnt_vary_compound_glyph() uses a strict greater-than comparison instead of greater-than-or-equal, allowing a crafted TrueType variable font to bypass the check and trigger a heap-based out-of-bounds read via memcpy. An attacker can deliver a malicious font file via email, EWW (Emacs Web Wowser), or documents with custom faces, causing Emacs to load it. This exposes heap memory contents which can be later used to defeat ASLR.

This issue was fixed in commit 95ab9ef627b212d74d321c5bbb5b56a1be7b9fbe

Weakness: CWE-193 (Off-by-one Error)

## Which versions are affected by CVE-2026-71391?


## How do I fix CVE-2026-71391?

No fix has been published for CVE-2026-71391 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-71391 being exploited?

There is no known exploitation of CVE-2026-71391 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-71391 and fix it if it is affected.

What it is: CVE-2026-71391 is a medium-severity memory corruption vulnerability in GNU Emacs, published on 10 Aug 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: There is no known exploitation of CVE-2026-71391 in the wild and no public exploit code.

Affected product: GNU Emacs. 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-2026-71391/ (Markdown: https://insights.sbomify.com/CVE-2026-71391/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-71391
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-71391
- OSV: https://osv.dev/vulnerability/CVE-2026-71391

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-71391/
Summaries are generated and may contain mistakes; the official description above is the record.