How severe is CVE-2019-8955?

CVE-2019-8955 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2019-8955 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 5% (91st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2019-8955?

CVE-2019-8955 primarily affects Torproject Tor. In total, 18 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2019-8955?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2019-8955 published?

CVE-2019-8955 was published on 2019-02-21 and last updated on 2026-06-17.

CVE-2019-8955

CVE-2019-8955 is a high-severity vulnerability in Torproject Tor with a CVSS 3.x base score of 7.5. 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-770.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 5% (91st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-770
Affected product: Torproject Tor
Published: 2019-02-21
Last modified: 2026-06-17

Description

In Tor before 0.3.3.12, 0.3.4.x before 0.3.4.11, 0.3.5.x before 0.3.5.8, and 0.4.x before 0.4.0.2-alpha, remote denial of service against Tor clients and relays can occur via memory exhaustion in the KIST cell scheduler.

Frequently asked questions

What is CVE-2019-8955?: In Tor before 0.3.3.12, 0.3.4.x before 0.3.4.11, 0.3.5.x before 0.3.5.8, and 0.4.x before 0.4.0.2-alpha, remote denial of service against Tor clients and relays can occur via memory exhaustion in the KIST cell scheduler.
How severe is CVE-2019-8955?: CVE-2019-8955 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2019-8955 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 5% (91st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2019-8955?: CVE-2019-8955 primarily affects Torproject Tor. In total, 18 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2019-8955?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2019-8955 published?: CVE-2019-8955 was published on 2019-02-21 and last updated on 2026-06-17.

References

Affected products (18)

cpe:2.3:a:torproject:tor:*:*:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.0:alpha-dev:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.1:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.2:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.3:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.4:rc:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.5:rc:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.6:rc:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.4.7:rc:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.0:alpha-dev:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.1:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.2:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.3:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.4:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.5:alpha:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.6:rc:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.3.5.7:*:*:*:*:*:*:*
cpe:2.3:a:torproject:tor:0.4.0.1:alpha:*:*:*:*:*:*

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