---
title: "CVE-2026-77640\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2026-77640?format=md
keywords: index, follow
---

# CVE-2026-77640

Publication date 20 August 2026

Last updated 2 September 2026

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**3.7 · Low**

[Score breakdown](https://ubuntu.com/security/CVE-2026-77640?format=md#impact-score)

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## Description

tor before 0.4.9.9 was prone to an infinite loop when decompressing a
truncated zlib/gzip stream with done=1. A truncated stream never reaches
Z\_STREAM\_END, causing zlib to return Z\_BUF\_ERROR with no input remaining,
which buf\_add\_compress() mistook for a full output buffer and retried
forever. Fixed by returning TOR\_COMPRESS\_ERROR in that case so the caller
can abort cleanly. This is TROVE-2026-021.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| tor | 26.04 LTS resolute | Needs evaluation |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| 18.04 LTS bionic | Needs evaluation |
| 16.04 LTS xenial | Needs evaluation |
| 14.04 LTS trusty | Needs evaluation |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

3.7 · Low

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | High |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | None |
  | Integrity impact | None |
  | Availability impact | Low |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 3.7 · Low |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-77640)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-77640)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-77640)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-77640)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-77640>
* <https://gitlab.torproject.org/tpo/core/tor/-/work_items/41274>