EUVD-2026-63665
GHSA-36cc-rhpv-jrxc
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessReach directory port of vulnerable tor
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DeliverySubmit crafted consensus/detached signature
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ExploitUnexpected signature digest type parsed
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ExecutionOut-of-bounds write corrupts memory
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ImpactDirectory authority crash / consensus disruption
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, write limits
MITRE ATT&CK
2 techniques across 2 tactics: Execution, Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Exploitation requires delivering a consensus document or detached signature that specifies an unexpected/unrecognized signature digest type to a tor instance running a version from 0.2.8.2-alpha up to before 0.4.9.9, so that the malformed material is parsed. Realistic impact is limited by role: the vendor states the effect is minor for most Tor roles (relays/clients) and only potentially major for directory authorities, which are the components that generate and exchange detached signatures. There is no user-interaction or authentication prerequisite per the CVSS vector (PR:N/UI:N), but the practical attack surface is narrowed to whoever can submit directory/signature material to a vulnerable role - most acutely a directory authority peer. |
| Impact | The vendor CVSS of 9.3 (AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:H) reflects an unauthenticated, network-reachable memory-corruption bug with a scope change and high availability impact, yet the EPSS probability is only 0.19% (9th percentile) and there is no known public exploit or KEV listing - signals that point to a serious latent bug rather than one under active mass exploitation. The vendor itself scopes the real-world impact narrowly: minor for most Tor roles, but potentially major for directory authorities, which are a small, well-known set of high-value hosts. This tension between a 9.3 score and low EPSS is best read as targeted, high-consequence risk concentrated on directory authorities rather than broad opportunistic exploitation, so any organization operating a directory authority or a heavily-relied-upon relay should prioritize patching even though the aggregate exploitation probability is low. Confidentiality impact is assessed as none by the vector; the primary danger is crash/DoS (A:H) with limited integrity impact (I:L), consistent with an out-of-bounds write in a parser. |
| Exploit ScenarioDerived | An attacker able to feed directory material to a Tor directory authority (e.g. a malicious or compromised peer authority, or a party positioned to submit a detached signature) crafts a consensus or detached signature carrying an unexpected signature digest type. When the authority parses it, the out-of-bounds write corrupts memory, most plausibly crashing the process and disrupting consensus formation. No public proof-of-concept has been identified. |
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Alert meAnalysisAIv2 – Sep 08, 2026
Out-of-bounds write in The Tor Project's tor daemon (0.2.8.2-alpha through versions before 0.4.9.9) can be triggered when the software parses a consensus document or detached signature containing an unexpected signature digest type (TROVE-2026-019, CWE-787). The flaw is minor for most Tor roles but potentially severe for directory authorities, which routinely exchange detached signatures. Fixed in 0.4.9.9; EPSS is low (0.19%, 9th percentile) and no public exploit identified at time of analysis.
Earlier versions of this analysis (1)
Out-of-bounds write in Tor's consensus and detached signature parser allows remote, unauthenticated network peers to trigger memory corruption by supplying a document with an unexpected signature digest type. All Tor releases before 0.4.9.9 are affected; impact is minor for relay and client nodes but potentially major for directory authorities, whose compromise could disrupt or undermine the integrity of the network-wide consensus. No public exploit code or CISA KEV listing has been identified at time of analysis, though the network-reachable attack vector and scope change in the CVSS vector (S:C) warrant urgent patching for directory authority operators specifically.
RemediationAI
Vendor-released patch: upgrade to tor 0.4.9.9 or later, which corrects the signature-digest-type parsing (see the 0.4.9.9 ChangeLog at https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog). Directory authority operators should treat this as the top priority given the vendor's note that impact is potentially major for that role. Where immediate upgrade is not possible for a directory authority, restrict which hosts can deliver detached signatures/consensus material to the authority's directory ports (peer directory authorities only) to reduce the set of parties able to submit crafted input - with the trade-off that overly tight filtering can disrupt normal consensus voting if a legitimate peer's address changes. For ordinary relays and clients the vendor assesses impact as minor, so a standard maintenance upgrade to 0.4.9.9 is sufficient. No reliable in-place workaround short of upgrading is documented.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Tor relies on signed consensus documents and detached signatures to establish the network's shared view of the relay directory; directory authorities generate and exchange these detached signatures, and every relay/client validates the resulting consensus. The vulnerability lies in the signature-parsing code path, which mishandles an unexpected/unrecognized signature digest type and writes past the bounds of a buffer (CWE-787, out-of-bounds write). The affected component is torproject:tor (cpe:2.3:a:torproject:tor). Because parsing occurs while processing directory material received over the network, malformed input reaches the vulnerable routine before full validation completes, which is characteristic of memory-corruption bugs in document/protocol parsers.
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:H
Malformed directory material is parsed without authentication over the network (AV:N/PR:N/UI:N); the OOB write primarily crashes the daemon (A:H) with limited integrity effect (I:L) and no confidentiality loss (C:N), with scope change (S:C) as parsing affects the directory subsystem.
Primary rating from Vendor (mitre).
CVSS VectorNVD
Lifecycle Timeline
4DescriptionNVD
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. This is TROVE-2026-019.
Executive ViewAI
A memory-corruption vulnerability in Tor daemon before version 0.4.9.9 can be triggered during consensus-document parsing. Organizations operating Tor directory authorities face heightened risk, as compromise of these trusted nodes could undermine network-routing integrity and service availability.
Apply vendor patch: Upgrade Tor daemon to version 0.4.9.9 or later.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.
Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.
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