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Response snapshot Nov 2, 2026, 19:26 UTC

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VulnerabilityCVE-2019-1543

ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation.

ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation. RFC 7539 specifies that the nonce value (IV) should be 96 bits (12 bytes). OpenSSL allows a variable nonce length and front pads the nonce with 0 bytes if it is less than 12 bytes.

At a glance

Exploited
Not known
Severity
7.4 High (CVSS 3.0)
Chance of exploitation
Not estimated
Sources
2 independent sources

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2019-1543 (opens a new tab)

What happened

ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation. RFC 7539 specifies that the nonce value (IV) should be 96 bits (12 bytes). OpenSSL allows a variable nonce length and front pads the nonce with 0 bytes if it is less than 12 bytes. However it also incorrectly allows a nonce to be set of up to 16 bytes.

In this case only the last 12 bytes are significant and any additional leading bytes are ignored. It is a requirement of using this cipher that nonce values are unique. Messages encrypted using a reused nonce value are susceptible to serious confidentiality and integrity attacks.

If an application changes the default nonce length to be longer than 12 bytes and then makes a change to the leading bytes of the nonce expecting the new value to be a new unique nonce then such an application could inadvertently encrypt messages with a reused nonce. Additionally the ignored bytes in a long nonce are not covered by the integrity guarantee of this cipher.

Any application that relies on the integrity of these ignored leading bytes of a long nonce may be further affected. Any OpenSSL internal use of this cipher, including in SSL/TLS, is safe because no such use sets such a long nonce value. However user applications that use this cipher directly and set a non-default nonce length to be longer than 12 bytes may be vulnerable. OpenSSL versions 1.1.1 and 1.1.

Continue reading

0 are affected by this issue. Due to the limited scope of affected deployments this has been assessed as low severity and therefore we are not creating new releases at this time. Fixed in OpenSSL 1.1.1c (Affected 1.1.1-1.1.1b). Fixed in OpenSSL 1.1.0k (Affected 1.1.0-1.1.0j).

Scores and how they were measured

CVSS base severity

7.4

Version 3.0As of

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2019-1543 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    Vendor advisory (via NVD references) (opens a new tab)

    The vendor advisory referenced by the CVE record, for affected versions and fixes.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  4. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  5. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 2). ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation. (CVE-2019-1543). https://kevwire.com/record/CVE-2019-1543

MLA

"ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation. (CVE-2019-1543)." KEVWire, 2 Nov. 2026, kevwire.com/record/CVE-2019-1543.

Chicago

KEVWire. "ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation. (CVE-2019-1543)." Last modified November 2, 2026. https://kevwire.com/record/CVE-2019-1543.

Evidence summary (plain text)

ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation. (Mar 6, 2019).
ChaCha20-Poly1305 is an AEAD cipher, and requires a unique nonce input for every encryption operation. RFC 7539 specifies that the nonce value (IV) should be 96 bits (12 bytes). OpenSSL allows a variable nonce length and front pads the nonce with 0 bytes if it is less than 12 bytes. However it also incorrectly allows a nonce to be set of up to 16 bytes. In this case only the last 12 bytes are significant and any additional leading bytes are ignored. It is a requirement of using this cipher that nonce values are unique.
CVSS 7.4 (version 3.0; evidence as of Nov 2, 2026; https://nvd.nist.gov/vuln/detail/CVE-2019-1543).
Sources:
NVD CVE-2019-1543: https://nvd.nist.gov/vuln/detail/CVE-2019-1543
Vendor advisory (via NVD references): https://www.openssl.org/news/secadv/20190306.txt
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-02T17:56:05.581Z&lastModEndDate=2026-11-02T19:25:57.888Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-02T17:21:00.248Z&lastModEndDate=2026-11-02T18:55:57.389Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-02T16:46:03.426Z&lastModEndDate=2026-11-02T18:20:57.848Z&resultsPerPage=500&startIndex=0
Record ID: CVE-2019-1543.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 2, 2026, 19:25 UTC. Ingestion is not an independent editorial investigation.

NVD status: Modified. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

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Record details

Record detail