Tor before 0.4.9.10 did not reject a CONFLUXLINK cell that arrives on a circuit which already has attached streams. A malicious client could send a RELAYCOMMANDBEGIN before the CONFLUXLINK on the same circuit, attaching an exit stream that would later end up orphan leaving a dangling circuit back-pointer and a use-after-free (UAF) when the circuit is freed. This is TROVE-2026-025.
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 ZSTREAMEND, causing zlib to return ZBUFERROR with no input remaining, which bufaddcompress() mistook for a full output buffer and retried forever. Fixed by returning TORCOMPRESSERROR in that case so the caller can abort cleanly. This is TROVE-2026-021.
Tor before 0.4.9.9 was prone to a compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compression bomb check entirely. This is TROVE-2026-022.
Tor before 0.4.9.11 is prone to a race condition where in just the right circumstances a rendezvous point could man-in-the-middle (impersonate) the onion service that the client was trying to reach.
Tor before 0.4.9.7, when circuit queue memory pressure exists, can experience a client crash because of a double close of a circuit, aka TROVE-2026-009.
Tor before 0.4.9.7 has a NULL pointer dereference when a CERT cell is received out of order, aka TROVE-2026-006.
Tor before 0.4.9.7 has an out-of-bounds read when an END, a TRUNCATE, or a TRUNCATED cell lacks a reason in its payload, aka TROVE-2026-011.
Tor before 0.4.9.7 can attempt or accept BEGINDIR via conflux legs, aka TROVE-2026-008.
Tor before 0.4.9.7 mishandles accounting of the conflux out-of-order queue during the clearing of a queue, aka TROVE-2026-010.
Tor before 0.4.9.7 has an out-of-bounds read by one byte via a malformed BEGIN cell, aka TROVE-2026-007.
From diffing 0.4.9.6 and 0.4.9.7 [0]: +Changes in version 0.4.9.7 - 2026-05-06 + This is a security release fixing several major bugfixes that were reported + in the past weeks. Huge thanks to everyone that reported these issues! We + strongly recommend upgrading as soon as possible. + + o Major bugfixes (cell handling): + - Fix out-of-bounds read (OOB) when END, TRUNCATE and TRUNCATED cell + have no reason in their payload. TROVE-2026-011. Found by Found by + Brian Carpenter (geeknik). Fixes bug 41254; bugfix + on 0.1.1.1-alpha. + + o Major bugfixes (conflux): + - Do not attempt or accept BEGINDIR via conflux legs. TROVE-2026- + 008. Credit to Anas Cherni from Calif.io in collaboration with + Claude and Anthropic Research. Fixes bug 41243; bugfix + on 0.4.8.1-alpha. + + o Major bugfixes (conflux, relay): + - Adjust conflux out-of-order queue accounting when clearing a + queue. TROVE-2026-010. Found by aptupdate. Fixes bug 41251; bugfix + on 0.4.8.1-alpha. + + o Major bugfixes (pathbias): + - Fix a client-side crash caused by double-close of a circuit while + under circuit queue memory pressure. TROVE-2026-009. Found by + cypherpunks. Fixes bug 41237; bugfix on 0.3.3.6-rc. + + o Major bugfixes (relay): + - Fix null pointer dereference when receiving a CERT cell out of + order. TROVE-2026-006. Found by Fwame. Fixes bug 41240; bugfix + on 0.2.4.4-alpha. + + o Major bugfixes (relay, onion service): + - Fix off-by-one out-of-bounds read if a malformed BEGIN cell is + received. TROVE-2026-007. Found by Flanagan. Fixes bug 41245; + bugfix on 0.2.4.7-alpha. + + o Minor features (fallbackdir): + - Regenerate fallback directories generated on May 06, 2026. + + o Minor features (geoip data): + - Update the geoip files to match the IPFire Location Database, as + retrieved on 2026/05/06. +
The referenced bugs are private, so no more details are available yet. There were several recent other security releases too for Tor.
[0] https://gitlab.torproject.org/tpo/core/tor/-/blob/tor-0.4.9.7/ReleaseNotes#L5
The SafeSocks option in Tor before 0.4.7.13 has a logic error in which the unsafe SOCKS4 protocol can be used but not the safe SOCKS4a protocol, aka TROVE-2022-002.
In Tor before 0.3.3.12, 0.3.4.x before 0.3.4.11, 0.3.5.x before 0.3.5.8, and 0.4.x before 0.4.0.2-alpha, remote denial of service against Tor clients and relays can occur via memory exhaustion in the KIST cell scheduler.
It was reported [1],[2] that Tor suffered from a denial of service vulnerability due to an error when handling SENDME cells. This could be exploited to cause excessive consumption of memory resources within an entry node.
This is fixed in upstream version 0.2.3.25 (git [3]).
[1] https://secunia.com/advisories/51329/ [2] https://trac.torproject.org/projects/tor/ticket/6252 [3] https://gitweb.torproject.org/arma/tor.git/commitdiff/b9b54568c0bb64c32bd0b362954bdbc8c1234b16
Tor before 0.2.3.24-rc allows remote attackers to cause a denial of service (assertion failure and daemon exit) by performing link protocol negotiation incorrectly.
Tor before 0.2.3.23-rc allows remote attackers to cause a denial of service (assertion failure and daemon exit) via a renegotiation attempt that occurs after the initiation of the V3 link protocol.
Tor before 0.2.4.23 and 0.2.5 before 0.2.5.6-alpha maintains a circuit after an inbound RELAYEARLY cell is received by a client, which makes it easier for remote attackers to conduct traffic-confirmation attacks by using the pattern of RELAY and RELAYEARLY cells as a means of communicating information about hidden service names.
The Hidden Service (HS) client implementation in Tor before 0.2.4.27, 0.2.5.x before 0.2.5.12, and 0.2.6.x before 0.2.6.7 allows remote servers to cause a denial of service (assertion failure and application exit) via a malformed HS descriptor.
The Hidden Service (HS) server implementation in Tor before 0.2.4.27, 0.2.5.x before 0.2.5.12, and 0.2.6.x before 0.2.6.7 allows remote attackers to cause a denial of service (assertion failure and daemon exit) via unspecified vectors.
bufpullup in Tor before 0.2.4.26 and 0.2.5.x before 0.2.5.11 does not properly handle unexpected arrival times of buffers with invalid layouts, which allows remote attackers to cause a denial of service (assertion failure and daemon exit) via crafted packets.
Tor before 0.2.4.26 and 0.2.5.x before 0.2.5.11 does not properly handle pending-connection resolve states during periods of high DNS load, which allows remote attackers to cause a denial of service (assertion failure and daemon exit) via crafted packets.
Tor before 0.2.8.9 and 0.2.9.x before 0.2.9.4-alpha had internal functions that were entitled to expect that buft data had NUL termination, but the implementation of or/buffers.c did not ensure that NUL termination was present, which allows remote attackers to cause a denial of service (client, hidden service, relay, or authority crash) via crafted data.
Tor before 0.2.8.12 might allow remote attackers to cause a denial of service (client crash) via a crafted hidden service descriptor.
Browser proxy settings can be bypassed by using the automount feature with autofs to create a mount point on the local file system. Content can be loaded from this mounted file system directly using a file: URI, bypassing configured proxy settings. Note: this issue only affects OS X in default configurations. On Linux systems, autofs must be installed for the vulnerability to occur and Windows is not affected.
The hidden-service feature in Tor before 0.3.0.8 allows a denial of service (assertion failure and daemon exit) in the connectionedgeprocessrelaycell function via a BEGINDIR cell on a rendezvous circuit.
The hidden-service feature in Tor before 0.3.0.8 allows a denial of service (assertion failure and daemon exit) in the relaysendendcellfromedge function via a malformed BEGIN cell.
The rendserviceintroestablished function in or/rendservice.c in Tor before 0.2.8.15, 0.2.9.x before 0.2.9.12, 0.3.0.x before 0.3.0.11, 0.3.1.x before 0.3.1.7, and 0.3.2.x before 0.3.2.1-alpha, when SafeLogging is disabled, allows attackers to obtain sensitive information by leveraging access to the log files of a hidden service, because uninitialized stack data is included in an error message about construction of an introduction point circuit.
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), which might allow remote attackers to defeat intended anonymity properties by leveraging the existence of large families.
An issue was discovered in Tor before 0.2.9.15, 0.3.1.x before 0.3.1.10, and 0.3.2.x before 0.3.2.10. The directory-authority protocol-list subprotocol implementation allows remote attackers to cause a denial of service (NULL pointer dereference and directory-authority crash) via a misformatted relay descriptor that is mishandled during voting.
A use-after-free issue was discovered in Tor 0.3.2.x before 0.3.2.10. It allows remote attackers to cause a denial of service (relay crash) because the KIST implementation allows a channel to be added more than once in the pending list.