# CVE-2026-77640: tor: tor before 0.4.9.9 was prone to an infinite loop when decompressing a truncated zlib/gzip  stream with done=1

CVE-2026-77640 is fixed in tor on 1 platform, first by DEBIAN-CVE-2026-77640, released August 21, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-77640
- Priority: Routine
- CVSS: 5.3 (medium)
- EPSS: 0.0038
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 20, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | tor Debian 12.15 (bookworm) | 0.4.9.9-1 | [DEBIAN-CVE-2026-77640](https://patchblox.com/security/data/fix/linux/debian-cve-2026-77640.md) | Aug 21, 2026 |
| Linux | tor Debian 13.5 (trixie) | 0.4.9.11-0+deb13u1 | [DEBIAN-CVE-2026-77640](https://patchblox.com/security/data/fix/linux/debian-cve-2026-77640.md) | Aug 21, 2026 |
| Linux | tor Debian 14 | 0.4.9.9-1 | [DEBIAN-CVE-2026-77640](https://patchblox.com/security/data/fix/linux/debian-cve-2026-77640.md) | Aug 21, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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