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High, CVSS 7.5

Remote DoS through unchecked IdList allocation in negentropy

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (negentropy 0.5.2, 0.4.4), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • crates.io negentropy

    Affected
    >= 0.2.0, < 0.4.4>= 0.5.0, < 0.5.2
    Fixed in
    0.4.4, 0.5.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

Summary The `negentropy` crate is vulnerable to denial-of-service through an unchecked, peer-controlled ID count in reconciliation messages. With the `std` feature enabled, which is the default configuration, a small malformed message can trigger an enormous memory allocation and terminate the application.

Details When processing an `IdList` range, the reconciliation parser uses the peer-provided ID count to reserve memory before checking whether the message contains the corresponding IDs: ```rust let mut their_elems: HashSet = HashSet::with_capacity(num_ids as usize); ``` An attacker can declare an arbitrarily large count without supplying any IDs. The allocation occurs before the parser reaches the ID-reading loop, which would otherwise reject the truncated message. With Rust's default allocation-error behavior, a failed allocation aborts the process rather than unwinding. Consequently, `catch_unwind` cannot contain the failure. Both `reconcile` and `reconcile_with_ids` reach…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from osv record RUSTSEC-2026-0365

Agent brief

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# Patch Next advisory brief: rustsec-2026-0365

Advisory: Remote DoS through unchecked `IdList` allocation in negentropy
IDs: rustsec-2026-0365
Record: https://patchnext.com/advisories/rustsec-2026-0365 (revision 1, source checked 23 Oct 2026, 22:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: negentropy 0.5.2, 0.4.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io negentropy: affected >= 0.2.0, < 0.4.4; >= 0.5.0, < 0.5.2; fixed in 0.4.4, 0.5.2

## Suggested inspection (read-only)
- crates.io negentropy: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on negentropy.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0365 (OSV record RUSTSEC-2026-0365 lists affected ranges: crates.io negentropy >=0.2.0 =0.5.0 <0.5.2 (fixed))

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