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CVE-2026-77640

Quick assessment

Affected
torproject Tor
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Tor 0.4.9.9 之前的版本中，当使用 解压缩截断的 zlib/gzip 流时，存在陷入无限循环的风险。由于截断的数据流永远不会达到 状态，zlib 会在无输入剩余的情况下返回 ，而 函数错误地将此错误解读为输出缓冲区已满，从而无限重试。该问题已通过在此种情况下返回 予以修复，以便调用方能够安全地中止操作。此漏洞对应编号为 TROVE-2026-021。

CVSS 3.7 · Low EPSS 0.21% · P12

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
torproject Tor 0.2.6.1-alpha< 0.4.9.9 affected
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I. Basic Information for CVE-2026-77640

Vulnerability Information
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Vulnerability Title
N/A
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1284
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
torproject Tor 0.2.6.1-alpha ~ 0.4.9.9 -

II. Public POCs for CVE-2026-77640

# POC Description Source Link Shenlong Link
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III. Intelligence Information for CVE-2026-77640

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Other References for CVE-2026-77640 (1)

Same Patch Batch · torproject · 2026-08-20 · 7 CVEs total

CVE-2026-77638 8.9 HIGH Tor <0.4.9.11中间人竞争条件漏洞
CVE-2026-77642 7.5 HIGH Tor <0.4.9.9共识解析越界写入漏洞
CVE-2026-77584 7.0 HIGH Tor <0.4.9.10 释放后使用漏洞
CVE-2026-77641 6.5 MEDIUM Tor 0.4.9.9前版本释放后空指针写入漏洞
CVE-2026-77587 5.9 MEDIUM Tor 0.4.9.11前存在释放后使用漏洞
CVE-2026-77639 5.3 MEDIUM Tor <0.4.9.9 压缩炸弹绕过漏洞

IV. Related Vulnerabilities

Same product: Tor
Same vendor: torproject
Same weakness: CWE-1284

V. Comments for CVE-2026-77640

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