GHSA-7gcf-g7xr-8hxj: serde_with KeyValueMap Serialization Panics On Empty Vulnerability

MODERATE
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CWE-20
Published
Advisory Summary

GHSA-7gcf-g7xr-8hxj is a MODERATE keyvaluemap serialization panics on empty vulnerability (CWE-20: Improper Input Validation) affecting serde_with libraries in the crates.io ecosystem. The issue involves keyvaluemap serialization panics on empty sequence or map entries. Remediation is available by upgrading affected packages to version 3.21.0.

GHSA-7gcf-g7xr-8hxj at a Glance

CVE Identifier N/A
GHSA Identifier GHSA-7gcf-g7xr-8hxj
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-20: Improper Input Validation
Affected Product serde_with
Package Ecosystem crates.io
Published Date
Last Updated

How to Fix GHSA-7gcf-g7xr-8hxj

To remediate this vulnerability, upgrade all affected serde_with dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

serde_with fixed: 3.21.0 
Upgrade serde_with to 3.21.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for serde_with

How to Check if You Are Affected

To determine whether your application is affected by GHSA-7gcf-g7xr-8hxj, inspect your project dependencies for serde_with:

inspect dependencies for serde_with

Analyze the terminal output to locate any version of serde_with in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.21.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In serde_with, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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 `#[serde_as(as = "KeyValueMap<_>")]` can be crashed by an empty inner sequence or map entry. ### Details The affected public surface includes: - Serialization of `#[serde_as(as = "KeyValueMap<_>")]` values through `serde_json::to_string` or any other Serde serializer` - Public `KeyValueMap` conversions for sequence and map-backed entries` The root cause is: The `KeyValueMap` serializer preallocating `Vec::with_capacity(len - 1)` or `Vec::with_capacity(len.unwrap_or(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 -> `serde_json::to_string` -> `KeyValueMap<TAs>::serialize_as` -> `SeqAsMapSerializer::{serialize_seq,serialize_map}` -> `Vec::with_capacity(len - 1)` or `Vec::with_capacity(len.unwrap_or(17) - 1)` -> panic Relevant source locations: - `serde_with/src/key_value_map.rs:590` - `serde_with/src/key_value_map.rs:599` - `serde_with/src/key_value_map.rs:613` - `serde_with/src/key_value_map.rs:632` - `serde_with/src/key_value_map.rs:648` ### PoC ```rust /* [dependencies] serde = {version = "*", features = ["derive"]} serde_with = "*" serde_json = "*" */ use serde::Serialize; use serde_with::{serde_as, KeyValueMap}; #[derive(Serialize)] #[serde(transparent)] struct Seq(Vec<String>); #[serde_as] #[derive(Serialize)] #[serde(transparent)] struct KVMap { #[serde_as(as = "KeyValueMap<_>")] foo: Vec<Seq>, } fn main() { let value = KVMap { foo: vec![Seq(Vec::new())], }; let _ = serde_json::to_string(&value).unwrap(); } ``` ### Impact A local attacker who can trigger serialization of attacker-controlled data through `KeyValueMap` can terminate the process, causing a denial of service.

GHSA-7gcf-g7xr-8hxj Affected serde_with Versions

1 component(s)
Fixed Versions:
3.21.0
Product / Package Ecosystem Affected Versions Fixed Version
serde_with
 crates.io
≥ 2.3.0
< 3.21.0
3.21.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/jonasbb/serde_with/security/advisories/GHSA-7gcf-g7xr-8hxj
serde_with Source Repository REPOSITORY
https://github.com/jonasbb/serde_with/pull/966
Security Fix Commit FIX COMMIT
https://github.com/jonasbb/serde_with/commit/c8a1d820ea25df01692b367058d587343e199389
serde_with Source Repository REPOSITORY
https://github.com/jonasbb/serde_with
serde_with Source Repository REPOSITORY
https://github.com/jonasbb/serde_with/compare/v2.2.0...v2.3.0
serde_with Release RELEASE
https://github.com/jonasbb/serde_with/releases/tag/v3.21.0

Frequently Asked Questions

What is GHSA-7gcf-g7xr-8hxj?
GHSA-7gcf-g7xr-8hxj is a security vulnerability in serde_with involving KeyValueMap serialization panics on empty sequence or map entries under CWE-20: Improper Input Validation.
Which serde_with versions are affected?
Affected versions include releases prior to 3.21.0 across affected packages: serde_with.
What version fixes GHSA-7gcf-g7xr-8hxj?
Upgrading to 3.21.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is serde_with affected?
Yes, serde_with is affected in releases prior to 3.21.0. Upgrade your dependency to 3.21.0 or later.
What CWE is associated with GHSA-7gcf-g7xr-8hxj?
GHSA-7gcf-g7xr-8hxj is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check crates.io dependencies for GHSA-7gcf-g7xr-8hxj?
Run the dependency tree command: 'inspect dependencies for serde_with'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7gcf-g7xr-8hxj",
  "modified" : "2026-08-31T14:18:13Z",
  "published" : "2026-07-15T22:41:01Z",
  "aliases" : [ ],
  "summary" : "serde_with: KeyValueMap serialization panics on empty sequence or map entries",
  "details" : "### Summary\n\nThe 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 `#[serde_as(as = \"KeyValueMap<_>\")]` can be crashed by an empty inner sequence or map entry.\n\n### Details\n\nThe affected public surface includes:\n\n- Serialization of `#[serde_as(as = \"KeyValueMap<_>\")]` values through `serde_json::to_string` or any other Serde serializer`\n- Public `KeyValueMap` conversions for sequence and map-backed entries`\n\nThe root cause is: The `KeyValueMap` serializer preallocating `Vec::with_capacity(len - 1)` or `Vec::with_capacity(len.unwrap_or(17) - 1)` before checking that the element actually contains the required first key field or item.\n\nThe vulnerable data/control flow is: attacker-controlled empty entry -> `serde_json::to_string` -> `KeyValueMap<TAs>::serialize_as` -> `SeqAsMapSerializer::{serialize_seq,serialize_map}` -> `Vec::with_capacity(len - 1)` or `Vec::with_capacity(len.unwrap_or(17) - 1)` -> panic\n\nRelevant source locations:\n\n- `serde_with/src/key_value_map.rs:590`\n- `serde_with/src/key_value_map.rs:599`\n- `serde_with/src/key_value_map.rs:613`\n- `serde_with/src/key_value_map.rs:632`\n- `serde_with/src/key_value_map.rs:648`\n\n### PoC\n\n```rust\n/*\n[dependencies]\nserde = {version = \"*\", features = [\"derive\"]}\nserde_with = \"*\"\nserde_json = \"*\"\n*/\n\nuse serde::Serialize;\nuse serde_with::{serde_as, KeyValueMap};\n\n#[derive(Serialize)]\n#[serde(transparent)]\nstruct Seq(Vec<String>);\n\n#[serde_as]\n#[derive(Serialize)]\n#[serde(transparent)]\nstruct KVMap {\n    #[serde_as(as = \"KeyValueMap<_>\")]\n    foo: Vec<Seq>,\n}\n\nfn main() {\n    let value = KVMap {\n        foo: vec![Seq(Vec::new())],\n    };\n    let _ = serde_json::to_string(&value).unwrap();\n}\n```\n\n### Impact\n\nA local attacker who can trigger serialization of attacker-controlled data through `KeyValueMap` can terminate the process, causing a denial of service.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "serde_with"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.3.0"
      }, {
        "fixed" : "3.21.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jonasbb/serde_with/security/advisories/GHSA-7gcf-g7xr-8hxj"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jonasbb/serde_with/pull/966"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jonasbb/serde_with/commit/c8a1d820ea25df01692b367058d587343e199389"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jonasbb/serde_with"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jonasbb/serde_with/compare/v2.2.0...v2.3.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jonasbb/serde_with/releases/tag/v3.21.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-15T22:41:01Z",
    "nvd_published_at" : null
  }
}