# CVE-2026-27628: pypdf has a possible infinite loop when loading circular /Prev entries in cross-reference streams

> An attacker can cause a denial of service via infinite loop by crafting a PDF with circular cross-reference entries, affecting applications using pypdf.

- **Severity:** Low 1.2 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U`)
- **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:** 25 Feb 2026
- **Updated:** 27 Feb 2026
- **Also known as:** CLSA-2026-1778460294, DEBIAN-CVE-2026-27628, GHSA-2rw7-x74f-jg35, PYSEC-2026-3005, ROOT-APP-PYPI-CVE-2026-27628, UBUNTU-CVE-2026-27628

## What is CVE-2026-27628?

CVE-2026-27628 is a low-severity denial of service vulnerability in Pypdf Project Pypdf, published on 25 Feb 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

pypdf is a free and open-source pure-python PDF library. Prior to 6.7.2, an attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires reading the file. This has been fixed in pypdf 6.7.2. As a workaround, one may apply the patch manually.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2026-27628?

3 open source packages ship an affected version, including pypdf. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `pypdf` | PyPI | All versions | 6.7.2 |
| `pypdf` | PyPI | All versions | 6.7.2 |
| `pypdf` | PyPI | All versions | 6.7.2 |

Products: Pypdf Project Pypdf.

## How do I fix CVE-2026-27628?

Upgrade pypdf to 6.7.2 or later.

## Is CVE-2026-27628 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27628 exists.

## Other vulnerabilities in Pypdf Project Pypdf

- [CVE-2026-102993](https://insights.sbomify.com/CVE-2026-102993/): pypdf: Possible large memory usage when retrieving Roman page labels (high 8.7)
- [CVE-2026-102994](https://insights.sbomify.com/CVE-2026-102994/): pypdf: Possible long runtimes/large memory usage when parsing indirect objects (high 8.7)
- [CVE-2026-102995](https://insights.sbomify.com/CVE-2026-102995/): pypdf: Possible large memory usage for large /ToUnicode streams (Follow-up 2) (high 8.7)
- [CVE-2026-102996](https://insights.sbomify.com/CVE-2026-102996/): pypdf: Possible large memory usage when parsing font data (high 8.7)
- [CVE-2026-102997](https://insights.sbomify.com/CVE-2026-102997/): pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up) (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27628 and fix it if it is affected.

What it is: CVE-2026-27628 is a low-severity denial of service vulnerability in Pypdf Project Pypdf, published on 25 Feb 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-2026-27628 exists.

Affected packages and fixed versions:
- pypdf (PyPI): affected all versions; fixed in 6.7.2
- pypdf (PyPI): affected all versions; fixed in 6.7.2
- pypdf (PyPI): affected all versions; fixed in 6.7.2

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-2026-27628/ (Markdown: https://insights.sbomify.com/CVE-2026-27628/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27628
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27628
- OSV: https://osv.dev/vulnerability/CVE-2026-27628

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27628/
Summaries are generated and may contain mistakes; the official description above is the record.