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

Status: published. Published: 2026-08-21. Updated: 2026-11-08.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/michaelrsweet/pdfio/commit/22b9afc800c5833f9e851e35938972bd4c76a357

## Affected products and versions

- michaelrsweet / pdfio (michaelrsweet/pdfio): ≥ 0; < 1.6.5 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 7.1 (high); 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; source: CNA: VulnCheck

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: 0.42% as of 2026-11-08; percentile 36.72%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-825

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/michaelrsweet/pdfio/releases/tag/v1.6.5 (CNA: VulnCheck; release-notes)

- https://github.com/michaelrsweet/pdfio/commit/22b9afc800c5833f9e851e35938972bd4c76a357 (CNA: VulnCheck; patch)

- https://www.vulncheck.com/advisories/pdfio-dangling-pointer-via-dictionary-string-formatting (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-77220; retrieved 2026-11-08; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-77220; retrieved 2026-11-08; source updated Not reported

Revision: 7a8a859ca255696114407ed26cd0ade67bbb2a559b37936660ea09190a608458

Canonical: https://y2.dev/cve/CVE-2026-77220

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