A bug in Tor's nodelist handling caused clients to permanently mark an exit relay as rejecting all traffic after receiving a single transient RELAY_END message, such as RESOURCELIMIT or HIBERNATING. This issue, introduced in Tor 0.2.3.1-alpha, allowed a third party to steer clients away from honest exits by exhausting an exit's sockets or sending a malicious END. The fix, which clears the 'rejects_all' flag when a new consensus is installed, is slated for the next stable release.
Why it matters This fix prevents a remote attacker from manipulating a client's usable exit set, which could otherwise lead to targeted denial of service or privacy leaks by biasing circuit selection.
The Tor Project has published Tor Browser 16.0.1 for Android, Windows, macOS, and Linux. This update includes a rebase onto Firefox 153.7.0esr, an update to Tor 0.4.9.16, and backported security fixes from Firefox 160.
Why it matters The release incorporates backported security fixes and updates to the underlying Tor and Firefox components.
Correction · Corrected an unsupported claim that ordinary relay operators must edit their configurations. The cited issues request removal of bastet's existing entry from the software.
The Tor development team reported that the operator of the bastet directory authority notified them that the machine is very plausibly compromised. The report states that bastet will be removed from the source code because its keys can no longer be trusted. The operator is expected to generate a new identity for the authority.
Why it matters The report says bastet's existing keys can no longer be trusted and requests removal of its current entry from the software.
The Tor Project released version 0.4.9.16 as an emergency update specifically for directory authorities. The release addresses a 'thundering herd' issue caused by new required protover values in the previous release, which was causing older clients to exit. It also includes a workaround for a bug where old clients failed to handle unparseable microdescriptors correctly when TAP keys were omitted.
Why it matters Scope and consequences remain subject to the linked upstream discussion.
The Arti project has an open issue titled 'Arti 2.8.0 release' which serves as an automatically scraped release checklist. The checklist includes steps for preparing confidential security patches, finalizing the changelog, and performing the release, with most items marked as complete. Post-release tasks are also listed, with some items remaining unchecked.
Why it matters Scope and consequences remain subject to the linked upstream discussion.
The Tails project has released version 7.16, which updates the bundled Tor Browser to 16.0 and the Tor client to 0.4.9.15. The release also includes a fix for OpenPGP support in Thunderbird. Users can upgrade their Tails USB sticks automatically from version 7.0 or later.
Why it matters This release provides updated security components and bug fixes for users relying on the Tails operating system for privacy.
The Tor Project has published Tor Browser 16.0 for Android, Windows, macOS, and Linux. The release updates the underlying Tor version to 0.4.9.15 and Firefox to 153.6.0esr, alongside various security and privacy adjustments such as disabling WebGPU and XSLT.
Why it matters Users should update to the latest version to receive the updated Tor and Firefox components and associated security fixes.
A community report on the tor-relays mailing list presents custom metrics from approximately 300 relays, identifying 30 distinct flood windows over 48 hours. The data indicates that descriptor fetching and HTTP-wait closures dominated the traffic, with one relay recording over 14 million fetches. The report notes that Tor 0.4.9.15 is expected to rate limit some of these requests, while a separate incident report describes a relay experiencing memory exhaustion and OOM termination during a similar period.
Why it matters The detailed metrics provide specific evidence of the traffic composition during recent network-wide resource exhaustion events, helping to distinguish between different types of flood attacks and validate the effectiveness of upcoming rate-limiting measures.
The Tor Project has released Tor Browser 16.0 for Desktop and Android, marking the first stable release based on Firefox ESR 153. This update includes a redesigned Settings interface, an option for generic window titles to prevent local snooping, and native support for 64-bit ARM Linux. The release also incorporates over 270 Bugzilla fixes from the annual ESR transition audit to address potential privacy and security impacts.
Why it matters This release updates the browser's core engine and introduces new privacy protections, such as generic window titles, while expanding platform support to 64-bit ARM Linux devices.
The Tor Project released version 0.4.9.15, a security update introducing new defenses against large volumes of directory requests. The release makes the HSDir flag sticky across restarts and updates directory authorities to require specific protocol capabilities, rendering Tor versions 0.4.8 and earlier incompatible with the network. Operators are advised to upgrade relays as soon as possible.
Why it matters The release includes critical DoS mitigations for relays and enforces protocol changes that will disconnect older clients from the network.
A security report identified an incorrect format string in Tor's consensus generation that the report says allowed three colluding directory authorities to prevent consensus publication. The project labeled the severity as low because exploitation requires control of multiple authorities. A comment by @arma states the issue is listed as fixed in 0.4.9.15 as of commit 407ccd28a.
Why it matters The report states that three colluding directory authorities can wedge consensus on all honest authorities, resulting in a network-wide DoS.
A security report filed via HackerOne describes a vulnerability in Arti's onion-service implementation where invalid proof-of-work requests cause unbounded growth of persistent replay logs. The report states that an unauthenticated attacker can append approximately 16 bytes of data per request without solving the proof of work, potentially leading to filesystem exhaustion and service unavailability. The issue remains open in the Arti development tracker.
Why it matters The report indicates that this vulnerability could allow an attacker to cause a denial of service against onion services by exhausting disk space, requiring operator intervention for recovery.
The Arti development team has completed the release checklist for the October 1, 2026 release. The process included merging confidential security patches from a private branch into the main branch, finalizing the changelog, and publishing the crates. A signed git tag was created to mark the release.
Why it matters This release includes confidential security patches that were merged into the main branch, indicating updates to the Arti software infrastructure.
A security report filed via HackerOne and published on GitLab describes a defect in Arti's rendezvous queue where a client sending no proof-of-work can evict a queued client that did. The report states this defeats the priority queue's purpose but notes it does not demonstrate a sustained denial of service. A maintainer commented that the issue is a bug but does not seem like a DoS issue, and a fix issue was created.
Why it matters The report states that the defect defeats the purpose of the priority queue, allowing clients to bypass proof-of-work requirements for queue admission.
A security report filed against Tor core identifies a vulnerability where a malformed `.auth_private` file causes Tor to log a near-complete v3 onion-service client-auth private key at WARN level, even when `SafeLogging` is enabled. The report states the issue affects Tor 0.3.5.1-alpha through 0.4.9.11 and the current main branch, with no fixed release identified. Public comments from Tor developers suggest a fix using safe logging.
Why it matters The report indicates that a lower-trust principal with access to Tor logs could obtain a near-complete private key from a malformed credential file, potentially compromising client authorization for v3 onion services.
A relay operator reports a sustained circuit-building DoS against their guard relay family starting June 25, 2026, characterized by an 8x sustained increase in open circuits and a 20x peak. The attack involved millions of near-idle circuits and onionskin processing spikes across multiple regions, with bandwidth increasing only 20%. While DoS defenses engaged and prevented TCP port exhaustion, EU relays shed 10-20% of real traffic due to capacity constraints.
Why it matters The report suggests the pattern is network-wide or family-targeted, and notes that EU relays shed 10-20% of real traffic.
A security report describes a CRLF injection vulnerability in the Tor daemon's SOCKS5 server, allowing an unauthenticated client to inject fake control event lines into the controller stream. The issue requires the non-default `AllowNonRFC953Hostnames=1` setting and was reported via HackerOne. A developer comment notes that a basic fix is available in a merge request targeted at the main branch, and the issue is currently closed.
Why it matters Controllers parsing events line-by-line may become desynchronized and act on forged state transitions if the non-default hostname setting is enabled.
Following a power outage on 2025-10-27, the Tor directory authority maatuska has been reporting substantially fewer relays with Guard flags in its votes compared to the network consensus. While initial reports showed a discrepancy of over 3,000 flags, recent data from November 2026 indicates the gap persists, with maatuska voting for roughly half the Guard relays of other authorities. The issue remains open.
Why it matters Scope and consequences remain subject to the linked upstream discussion.
