CVE-2019-11756Network attack vector

Browser crash via improper SFTKSession refcounting

Published Jan 8, 2020 · Updated Aug 4, 2024

Use-after-free in Firefox before 71 allows attackers to crash the browser through improper soft-token session object refcounting. The sftk_FreeSession path releases an SFTKSession while incorrect reference tracking can leave the freed object in use. Mozilla has not disclosed the input or action that reaches this cleanup path; the reported consequence is a browser crash likely limited to denial of service.

CVSS severity8.8
High
EPSS probability1.50%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Firefox before 71 allows attackers to crash the browser through improper soft-token session object refcounting. The sftk_FreeSession path releases an SFTKSession while incorrect reference tracking can leave the freed object in use. Mozilla has not disclosed the input or action that reaches this cleanup path; the reported consequence is a browser crash likely limited to denial of service.

The record

CVE
CVE-2019-11756
Published
Jan 8, 2020
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-416, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 8, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=before 71

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=before 71

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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