How severe is CVE-2026-77641?

CVE-2026-77641 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability high.

Is CVE-2026-77641 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (27th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-77641?

CVE-2026-77641 affects Torproject Tor. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-77641?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2026-77641 published?

CVE-2026-77641 was published on 2026-08-20 and last updated on 2026-09-08.

CVE-2026-77641

CVE-2026-77641 is a medium-severity vulnerability in Torproject Tor with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-252.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 0% (27th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-252
Affected product: Torproject Tor
Published: 2026-08-20
Last modified: 2026-09-08

Description

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.

Frequently asked questions

What is CVE-2026-77641?: 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.
How severe is CVE-2026-77641?: CVE-2026-77641 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability high.
Is CVE-2026-77641 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (27th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-77641?: CVE-2026-77641 affects Torproject Tor. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-77641?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2026-77641 published?: CVE-2026-77641 was published on 2026-08-20 and last updated on 2026-09-08.

References

https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog

Affected products (1)

cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*

More vulnerabilities in Torproject Tor

CVE-2026-77638 — High (CVSS 8.9): Tor before 0.4.9.11 is prone to a race condition where in just the right circumstances a rendezvous point could…
CVE-2026-77642 — High (CVSS 7.5): tor before 0.4.9.9 was prone to an out-of-bounds write when parsing a consensus or detached signature with unexpected…
CVE-2022-33903 — High (CVSS 7.5): Tor 0.4.7.x before 0.4.7.8 allows a denial of service via the wedging of RTT estimation.
CVE-2021-38385 — High (CVSS 7.5): Tor before 0.3.5.16, 0.4.5.10, and 0.4.6.7 mishandles the relationship between batch-signature verification and…
CVE-2021-34550 — High (CVSS 7.5): An issue was discovered in Tor before 0.4.6.5, aka TROVE-2021-006. The v3 onion service descriptor parsing allows…
CVE-2021-34549 — High (CVSS 7.5): An issue was discovered in Tor before 0.4.6.5, aka TROVE-2021-005. Hashing is mishandled for certain retrieval of…

All CVEs affecting Torproject Tor →

Other CWE-252 vulnerabilities

CVE-2025-66565 — Critical (CVSS 9.8): Fiber Utils is a collection of common functions created for Fiber. In versions 2.0.0-rc.3 and below, when the system's…
CVE-2023-52687 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: crypto: safexcel - Add error handling for…
CVE-2021-38171 — Critical (CVSS 9.8): adts_decode_extradata in libavformat/adtsenc.c in FFmpeg 4.4 does not check the init_get_bits return value, which is a…
CVE-2021-26955 — Critical (CVSS 9.8): An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because…
CVE-1999-0199 — Critical (CVSS 9.8): manual/search.texi in the GNU C Library (aka glibc) before 2.2 lacks a statement about the unspecified tdelete return…
CVE-2019-15900 — Critical (CVSS 9.8): An issue was discovered in slicer69 doas before 6.2 on certain platforms other than OpenBSD. On platforms without…

Browse all CWE-252 vulnerabilities →