EUVD-2026-63658
GHSA-r3c6-fj5w-6f75
Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Network-reachable via Tor protocol (AV:N), no auth required (PR:N), but high complexity to trigger send failure (AC:H); impact is crash only, so I drops to N.
Primary rating from Vendor (mitre).
CVSS VectorVendor: mitre
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Lifecycle Timeline
2DescriptionCVE.org
tor before 0.4.9.9 was prone to a NULL write after free when sending a CONFLUX_SWITCH cell fails. The return value of relay_send_command_from_edge() was ignored, so a send failure (which calls circuit_mark_for_close() and removes the leg via cfx_del_leg()) would go undetected, causing the caller to write to the now-freed current leg and resulting in a crash. This is TROVE-2026-017.
AnalysisAI
Use-after-free crash in Tor's conflux traffic-splitting code allows a remote unauthenticated attacker (per CVSS:3.1/AV:N/PR:N) to crash a Tor relay or client by triggering a CONFLUX_SWITCH cell send failure. The root cause is an unchecked return value from relay_send_command_from_edge(): when the send fails, the circuit is torn down and the leg freed via cfx_del_leg(), but the caller proceeds to write to that now-freed memory, causing a NULL write-after-free and process crash. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the target Tor instance is using the conflux subsystem (traffic multiplexing across circuit legs), which is the feature that processes CONFLUX_SWITCH cells. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 base score of 6.5 reflects a real but constrained threat: network-reachable (AV:N), no authentication (PR:N), but high attack complexity (AC:H). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker operating or compromising a Tor relay peer sends a crafted sequence that causes relay_send_command_from_edge() to fail during CONFLUX_SWITCH cell transmission to a target relay or client running Tor < 0.4.9.9. The failure silently frees the circuit leg, and the target's Tor process writes to the freed memory, crashing immediately. … |
| Remediation | Upgrade to Tor 0.4.9.9 or later, which contains the fix for TROVE-2026-017 as confirmed in the Tor Project ChangeLog (https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog). … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-252 – Unchecked Return Value
View allSame technique Denial Of Service
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External POC / Exploit Code
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