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GHSA-cq8v-f236-94qc

Rand is unsound with a custom logger using rand::rng()

No scoreFix available

GHSA-cq8v-f236-94qc is a vulnerability with no CVSS score yet in rand, published April 9, 2026. No source lists public exploit code. Fixed in rand 0.10.1.

What does this mean?
Severity
UnratedNo CVSS score yet
Exploit chance
UnscoredNo EPSS score yet
Exploitation
None knownNot on CISA’s or ENISA’s lists
Fixed in
0.10.1rand +4 more

Description

It has been reported (by @lopopolo) that the rand library is unsound (i.e. that safe code using the public API can cause Undefined Behaviour) when all the following conditions are met:

  • The log and thread_rng features are enabled
  • A custom logger is defined
  • The custom logger accesses rand::rng() (previously rand::thread_rng()) and calls any TryRng (previously RngCore) methods on ThreadRng
  • The ThreadRng (attempts to) reseed while called from the custom logger (this happens every 64 kB of generated data)
  • Trace-level logging is enabled or warn-level logging is enabled and the random source (the getrandom crate) is unable to provide a new seed

TryRng (previously RngCore) methods for ThreadRng use unsafe code to cast *mut BlockRng<ReseedingCore> to &mut BlockRng<ReseedingCore>. When all the above conditions are met this results in an aliased mutable reference, violating the Stacked Borrows rules. Miri is able to detect this violation in sample code. Since construction of aliased mutable references is Undefined Behaviour, the behaviour of optimized builds is hard to predict.

Affected packages

Affected packages
PackageAffectedFixed
rand
crates.io
0.10.0 to 0.10.0
0.10.1
rand
crates.io
0.9.0 up to 0.9.3
0.9.3
rand
crates.io
0.7.0 up to 0.8.6
0.8.6
rand
crates.io
0.10.0 up to 0.10.1
0.10.1
rand
crates.io
0.7.0 up to 0.8.6, 0.9.0 up to 0.9.3, 0.10.0 up to 0.10.1
0.8.60.9.30.10.1

What each source reports

GitHub AdvisoriesNo score

Rand is unsound with a custom logger using rand::rng()

It has been reported (by @lopopolo) that the rand library is unsound (i.e. that safe code using the public API can cause Undefined Behaviour) when all the following conditions are met:

  • The log and thread_rng features are enabled
  • A custom logger is defined
  • The custom logger accesses rand::rng() (previously rand::thread_rng()) and calls any TryRng (previously RngCore) methods on ThreadRng
  • The ThreadRng (attempts to) reseed while called from the custom logger (this happens every 64 kB of generated data)
  • Trace-level logging is enabled or warn-level logging is enabled and the random source (the getrandom crate) is unable to provide a new seed

TryRng (previously RngCore) methods for ThreadRng use unsafe code to cast *mut BlockRng<ReseedingCore> to &mut BlockRng<ReseedingCore>. When all the above conditions are met this results in an aliased mutable reference, violating the Stacked Borrows rules. Miri is able to detect this violation in sample code. Since construction of aliased mutable references is Undefined Behaviour, the behaviour of optimized builds is hard to predict.

Record
GHSA-cq8v-f236-94qc
Weakness
CWE-20
Updated
2026-11-02
OSVNo score

Rand is unsound with a custom logger using rand::rng()

It has been reported (by @lopopolo) that the rand library is unsound (i.e. that safe code using the public API can cause Undefined Behaviour) when all the following conditions are met:

  • The log and thread_rng features are enabled
  • A custom logger is defined
  • The custom logger accesses rand::rng() (previously rand::thread_rng()) and calls any TryRng (previously RngCore) methods on ThreadRng
  • The ThreadRng (attempts to) reseed while called from the custom logger (this happens every 64 kB of generated data)
  • Trace-level logging is enabled or warn-level logging is enabled and the random source (the getrandom crate) is unable to provide a new seed

TryRng (previously RngCore) methods for ThreadRng use unsafe code to cast *mut BlockRng<ReseedingCore> to &mut BlockRng<ReseedingCore>. When all the above conditions are met this results in an aliased mutable reference, violating the Stacked Borrows rules. Miri is able to detect this violation in sample code. Since construction of aliased mutable references is Undefined Behaviour, the behaviour of optimized builds is hard to predict.

Record
GHSA-cq8v-f236-94qc
Weakness
CWE-20
Updated
2026-11-02
OSVRUSTSEC-2026-0097No score

Rand is unsound with a custom logger using `rand::rng()`

It has been reported (by @lopopolo) that the rand library is unsound (i.e. that safe code using the public API can cause Undefined Behaviour) when all the following conditions are met:

  • The log and thread_rng features are enabled
  • A custom logger is defined
  • The custom logger accesses rand::rng() (previously rand::thread_rng()) and calls any TryRng (previously RngCore) methods on ThreadRng
  • The ThreadRng (attempts to) reseed while called from the custom logger (this happens every 64 kB of generated data)
  • Trace-level logging is enabled or warn-level logging is enabled and the random source (the getrandom crate) is unable to provide a new seed

TryRng (previously RngCore) methods for ThreadRng use unsafe code to cast *mut BlockRng<ReseedingCore> to &mut BlockRng<ReseedingCore>. When all the above conditions are met this results in an aliased mutable reference, violating the Stacked Borrows rules. Miri is able to detect this violation in sample code. Since construction of aliased mutable references is Undefined Behaviour, the behaviour of optimized builds is hard to predict.

Record
RUSTSEC-2026-0097
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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