CVE-2026-77640
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk12th percentile - higher than 12% of all known CVEs
Summary
Tor before 0.4.9.9 can enter an infinite loop when decompressing a truncated zlib/gzip stream with done=1. The truncated stream never reaches Z_STREAM_END, causing zlib to return Z_BUF_ERROR, which is mistaken for a full output buffer.
Risk Assessment
The infinite loop can cause a process hang, potentially leading to denial of service for the Tor service.
Recommendation
Upgrade to version 0.4.9.9 or later, which contains the fix.
Other vulnerabilities in Tor
See all- CVE-2016-1254High
Tor before 0.2.8.12 might allow remote attackers to cause a denial of service (client crash) via a crafted hidden service descriptor.
- CVE-2017-8823High
In Tor before version 0.2.5.16 and in versions 0.2.6 through 0.2.8 before 0.2.8.17, 0.2.9 before 0.2.9.14, 0.3.0 before 0.3.0.13, and 0.3.1 before 0.3.1.9, there is a use-after-free vulnerability in onion service v2 during intro-point expiration due to mismanagement of the expiring list in certain error cases.
- CVE-2017-8821High
In Tor before version 0.2.5.16 and in versions 0.2.6 through 0.2.8 before 0.2.8.17, 0.2.9 before 0.2.9.14, 0.3.0 before 0.3.0.13, and 0.3.1 before 0.3.1.9, an attacker can cause a denial of service (application hang) via crafted PEM input that signifies a public key requiring a password, triggering an attempt by the OpenSSL library to ask the user for the password.
- CVE-2017-8820High
In Tor before version 0.2.5.16 and in versions 0.2.6 through 0.2.8 before 0.2.8.17, 0.2.9 before 0.2.9.14, 0.3.0 before 0.3.0.13, and 0.3.1 before 0.3.1.9, remote attackers can cause a denial of service via a NULL pointer dereference, leading to application crash.
- CVE-2017-8819High
In Tor before version 0.2.5.16 and in versions 0.2.6 through 0.2.8 before 0.2.8.17, 0.2.9 before 0.2.9.14, 0.3.0 before 0.3.0.13, and 0.3.1 before 0.3.1.9, the replay-cache protection mechanism is ineffective for v2 onion services. An attacker can send many INTRODUCE2 cells to trigger this issue.
- CVE-2017-0377High
Tor 0.3.x before 0.3.0.9 has a guard-selection algorithm that only considers the exit relay, not the exit relay's family. This may allow remote attackers to defeat intended anonymity properties by leveraging the existence of large families.
- CVE-2017-0375High
The hidden-service feature in Tor before version 0.3.0.8 allows a denial of service (assertion failure and daemon exit) via a malformed BEGIN cell.
- CVE-2016-8860High
Tor versions before 0.2.8.9 and 0.2.9.x before 0.2.9.4-alpha had functions that expected buf_t data to be NUL terminated. The implementation in or/buffers.c did not ensure this termination, allowing remote attackers to cause a denial of service (client, hidden service, relay, or authority crash) via crafted data.
- CVE-2026-77642High
Tor before 0.4.9.9 was prone to an out-of-bounds write when parsing a consensus or detached signature with unexpected signature digest type. Impact is minor for most Tor roles, but potentially major for directory authorities.
- CVE-2026-77641Medium
Tor before 0.4.9.9 was prone to a NULL write after free when sending a CONFLUX_SWITCH cell fails. Ignoring the return value of relay_send_command_from_edge() leads to a crash.
Original NVD description (English source)
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.