# CVE-2026-77220: PDFio < 1.6.5 Dangling Pointer via Dictionary String-Formatting

> Attackers can corrupt document data or read sensitive information by exploiting a dangling pointer in PDFio's dictionary string formatting.

- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Aug 2026
- **Updated:** 1 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-77220, GHSA-2fr4-jfvm-chmp, UBUNTU-CVE-2026-77220

## What is CVE-2026-77220?

CVE-2026-77220 is a high-severity use after free vulnerability in michaelrsweet pdfio, published on 21 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

PDFio before 1.6.5 contains a dangling pointer vulnerability in the dictionary string-formatting function that stores a pointer to a stack-local buffer in the document dictionary without copying the string value. In multi-threaded or pooled-request environments, attackers or concurrent users can trigger stack memory reuse across requests, causing cross-tenant document content corruption by silently overwriting one caller's dictionary string values with another caller's data.

Weakness: CWE-825 (Expired Pointer Dereference)

## Which versions are affected by CVE-2026-77220?


## How do I fix CVE-2026-77220?

Upgrade to a fixed version.

## Is CVE-2026-77220 being exploited?

There is no known exploitation of CVE-2026-77220 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77220 and fix it if it is affected.

What it is: CVE-2026-77220 is a high-severity use after free vulnerability in michaelrsweet pdfio, published on 21 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-77220 in the wild and no public exploit code.

Affected product: michaelrsweet pdfio. 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-2026-77220/ (Markdown: https://insights.sbomify.com/CVE-2026-77220/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77220
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77220
- OSV: https://osv.dev/vulnerability/CVE-2026-77220

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77220/
Summaries are generated and may contain mistakes; the official description above is the record.