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GHSA-x5j2-g63m-f8g4

pqc_kyber KyberSlash: division timings depending on secrets

7.4 High

GHSA-x5j2-g63m-f8g4 is a high vulnerability (CVSS 7.4) in pqc_kyber, published December 1, 2023. No source lists public exploit code. No source names a fixed version.

What does this mean?
Severity
7.4 HighCVSS 3.1, GitHub Advisories
Exploit chance
UnscoredNo EPSS score yet
Exploitation
None knownNot on CISA’s or ENISA’s lists
Fixed in
No fix listedNo source names one

Description

Various Kyber software libraries in various environments leak secret information into timing, specifically because

  • these libraries include a line of code that divides a secret numerator by a public denominator,
  • the number of CPU cycles for division in various environments varies depending on the inputs to the division, and
  • this variation appears within the range of numerators used in these libraries.

The KyberSlash pages track which Kyber libraries have this issue, and include a FAQ about the issue.

Author

The KyberSlash pages were written by Daniel J. Bernstein. The FAQ originally said "I", but some people seemed to have trouble finding this authorship statement, so the FAQ now says "Bernstein" instead.

URL

The permanent link for the KyberSlash pages is https://kyberslash.cr.yp.to.

Mitigation status in pqc_kyber crate

The issues has not been resolved in the pqc_kyber crate. A third-party fork that mitigates this attack vector has been published as safe_pqc_kyber.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
None

Affected packages

Affected packages
PackageAffectedFixed
pqc_kyber
crates.io
through 0.7.1None known
pqc_kyber
crates.io
0.0.0-0 and laterNone known

What each source reports

GitHub Advisories Score used7.4

pqc_kyber KyberSlash: division timings depending on secrets

Various Kyber software libraries in various environments leak secret information into timing, specifically because

  • these libraries include a line of code that divides a secret numerator by a public denominator,
  • the number of CPU cycles for division in various environments varies depending on the inputs to the division, and
  • this variation appears within the range of numerators used in these libraries.

The KyberSlash pages track which Kyber libraries have this issue, and include a FAQ about the issue.

Author

The KyberSlash pages were written by Daniel J. Bernstein. The FAQ originally said "I", but some people seemed to have trouble finding this authorship statement, so the FAQ now says "Bernstein" instead.

URL

The permanent link for the KyberSlash pages is https://kyberslash.cr.yp.to.

Mitigation status in pqc_kyber crate

The issues has not been resolved in the pqc_kyber crate. A third-party fork that mitigates this attack vector has been published as safe_pqc_kyber.

Record
GHSA-x5j2-g63m-f8g4
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated
2026-11-02
OSV7.4

pqc_kyber KyberSlash: division timings depending on secrets

Various Kyber software libraries in various environments leak secret information into timing, specifically because

  • these libraries include a line of code that divides a secret numerator by a public denominator,
  • the number of CPU cycles for division in various environments varies depending on the inputs to the division, and
  • this variation appears within the range of numerators used in these libraries.

The KyberSlash pages track which Kyber libraries have this issue, and include a FAQ about the issue.

Author

The KyberSlash pages were written by Daniel J. Bernstein. The FAQ originally said "I", but some people seemed to have trouble finding this authorship statement, so the FAQ now says "Bernstein" instead.

URL

The permanent link for the KyberSlash pages is https://kyberslash.cr.yp.to.

Mitigation status in pqc_kyber crate

The issues has not been resolved in the pqc_kyber crate. A third-party fork that mitigates this attack vector has been published as safe_pqc_kyber.

Record
GHSA-x5j2-g63m-f8g4
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated
2026-11-02
OSVRUSTSEC-2023-00797.4

KyberSlash: division timings depending on secrets

Various Kyber software libraries in various environments leak secret information into timing, specifically because

  • these libraries include a line of code that divides a secret numerator by a public denominator,
  • the number of CPU cycles for division in various environments varies depending on the inputs to the division, and
  • this variation appears within the range of numerators used in these libraries.

The KyberSlash pages track which Kyber libraries have this issue, and include a FAQ about the issue.

Author

The KyberSlash pages were written by Daniel J. Bernstein. The FAQ originally said "I", but some people seemed to have trouble finding this authorship statement, so the FAQ now says "Bernstein" instead.

URL

The permanent link for the KyberSlash pages is https://kyberslash.cr.yp.to.

Mitigation status in pqc_kyber crate

The issue has not been resolved in the upstream pqc_kyber crate.

A third-party fork that mitigates this attack vector has been published as safe_pqc_kyber.

Alternatives

The ml-kem crate is a maintained alternative pure Rust implementation of ML-KEM / Kyber.

Record
RUSTSEC-2023-0079
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated
2026-11-02

History

History
RecordedChangedSources
first indexedGitHub Advisories, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

References

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