Cyber Resilience

CVE-2026-77584

Torproject Tor ≤ 0.4.9.10

Published
20 August 2026
Modified
16 September 2026
Patch / advisory
View advisory
CVSS Score v3.1 7.0
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L
EPSS Score 0.0018 8th percentile
Risk Priority 50 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-77584 is a high-severity Incorrect Synchronization (CWE-821) vulnerability in Torproject Tor. Its CVSS base score is 7.0 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SC-4 (Information in Shared System Resources) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

Tor before 0.4.9.10 did not reject a CONFLUX_LINK cell that arrives on a circuit which already has attached streams. A malicious client could send a RELAY_COMMAND_BEGIN before the CONFLUX_LINK on the same circuit, attaching an exit stream that would later…

more

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.

CWE(s)
CWE-821

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

Affected Assets

torproject
tor
≤ 0.4.9.10

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SC-4 Information in Shared System Resources partial match

SC-4 directly requires preventing unintended information transfer through shared resources, structurally blocking the concurrent unsynchronized access described by CWE-821.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 partial match
prevents

Secure SDLC practices directly require correct concurrency controls and synchronization primitives to prevent race conditions.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC practices include concurrency and synchronization requirements that reduce race conditions.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate proper locking and thread-safety controls.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles address concurrent access and resource synchronization.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly require correct synchronization primitives and thread-safety.

A.8.29 Security testing in development and acceptance partial match
finds

Security testing can detect synchronization flaws before production deployment.

References