CVE-2026-77640
LOWDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Exploit Intelligence
Low risk: more likely to be exploited than 12% of all known CVEs.
References
Related Vulnerabilities
Other CWE-1284 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2022-20699 | Critical | 10.0 | 72% | KEV | - |
| CVE-2021-43267 | Critical | 9.8 | 58% | - | Fix |
| CVE-2022-31629 | Medium | 6.5 | 49% | - | Fix |
| CVE-2025-9316 | Unscored | - | 36% | - | - |
| CVE-2022-36620 | High | 7.5 | 23% | - | - |
| CVE-2008-1440 | High | 7.1 | 23% | - | - |
Common questions
How do I fix CVE-2026-77640?
Upgrade tor on debian 12 to 0.4.9.9-1 or later.
Is CVE-2026-77640 being actively exploited?
Not that we know of. CVE-2026-77640 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.21% is the estimated probability that it will be exploited in the next 30 days. That is higher than 12% of all scored CVEs.
How severe is CVE-2026-77640?
CVE-2026-77640 has a CVSS v3 base score of 3.7, rated low. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-77640 affect?
Published advisories record a fix for tor (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2026-77640
Markdown
[](https://tridentstack.com/cve/CVE-2026-77640)HTML
<a href="https://tridentstack.com/cve/CVE-2026-77640"><img src="https://tridentstack.com/cve/badge/CVE-2026-77640.svg" alt="CVE-2026-77640"></a>Find and fix vulnerabilities across your fleet
TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.
This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-21.