CVE-2019-11759Public exploitNetwork attack vector

Code execution or crash via oversized HKDF output

Published Jan 8, 2020 · Updated Aug 4, 2024

Stack buffer overflow in Mozilla NSS allows remote attackers to execute code or crash affected Firefox, Firefox ESR, and Thunderbird releases. NSC_DeriveKey passes an oversized HKDF-SHA1 result through HMAC_Finish to SHA1_End, which writes four HMAC bytes beyond the 576-byte key_block stack buffer. A user must process attacker-controlled content that invokes WebCrypto HKDF; successful exploitation affects the client process, and the published proof of concept demonstrates a crash under AddressSanitizer.

CVSS severity8.8
High
EPSS probability1.80%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack buffer overflow in Mozilla NSS allows remote attackers to execute code or crash affected Firefox, Firefox ESR, and Thunderbird releases. NSC_DeriveKey passes an oversized HKDF-SHA1 result through HMAC_Finish to SHA1_End, which writes four HMAC bytes beyond the 576-byte key_block stack buffer. A user must process attacker-controlled content that invokes WebCrypto HKDF; successful exploitation affects the client process, and the published proof of concept demonstrates a crash under AddressSanitizer.

The record

CVE
CVE-2019-11759
Published
Jan 8, 2020
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-120, T1203
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 70

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=before 70
Mozilla · Thunderbirdversion=before 68.2
Mozilla · Firefox ESRversion=before 68.2

Published CVSS scores

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

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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