serde_with: KeyValueMap serialization panics on empty sequence or map entries

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.1 · CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary The public KeyValueMap serializer assumes that each mapped element has at least one field or item to use as the map key, but it subtracts 1 from the caller-visible length before validating that assumption. An application that serializes attacker-controlled data through #[serdeas(as = "KeyValueMap<")] can be crashed by an empty inner sequence or map entry. Details The affected public surface includes: - Serialization of #[serdeas(as = "KeyValueMap<")] values through serdejson::tostring or any other Serde serializer - Public KeyValueMap conversions for sequence and map-backed entries The root cause is: The KeyValueMap serializer preallocating Vec::withcapacity(len - 1) or Vec::withcapacity(len.unwrapor(17) - 1) before checking that the element actually contains the required first key field or item. The vulnerable data/control flow is: attacker-controlled empty entry - serdejson::tostring - KeyValueMap<TAs::serializeas - SeqAsMapSerializer::{serializeseq,serializemap} -…

Published by the source

15 Jul 2026, 22:41 UTC

Last modified by the source

31 Aug 2026, 14:18 UTC

Source last checked

26 Oct 2026, 15:43 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-7gcf-g7xr-8hxj

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# Patch Next advisory brief: GHSA-7gcf-g7xr-8hxj

Advisory: serde_with: KeyValueMap serialization panics on empty sequence or map entries
IDs: GHSA-7gcf-g7xr-8hxj
Record: https://patchnext.com/advisories/ghsa-7gcf-g7xr-8hxj (revision 1, source checked 26 Oct 2026, 15:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: serde_with 3.21.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io serde_with: affected >= 2.3.0, < 3.21.0; fixed in 3.21.0

## Suggested inspection (read-only)
- crates.io serde_with: 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 serde_with.
- 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://github.com/advisories/GHSA-7gcf-g7xr-8hxj (GitHub-reviewed advisory GHSA-7gcf-g7xr-8hxj lists affected ranges: crates.io serde_with >=2.3.0 <3.21.0)

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