GHSA-7GCF-G7XR-8HXJ
Vulnerability from github – Published: 2026-07-15 22:41 – Updated: 2026-08-31 14:18Summary
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 throughserde_json::to_stringor any other Serde serializer` - Public
KeyValueMapconversions 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:590serde_with/src/key_value_map.rs:599serde_with/src/key_value_map.rs:613serde_with/src/key_value_map.rs:632serde_with/src/key_value_map.rs:648
PoC
/*
[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.
{
"affected": [
{
"package": {
"ecosystem": "crates.io",
"name": "serde_with"
},
"ranges": [
{
"events": [
{
"introduced": "2.3.0"
},
{
"fixed": "3.21.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-20"
],
"github_reviewed": true,
"github_reviewed_at": "2026-07-15T22:41:01Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"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\u003c_\u003e\")]` 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\u003c_\u003e\")]` 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 -\u003e `serde_json::to_string` -\u003e `KeyValueMap\u003cTAs\u003e::serialize_as` -\u003e `SeqAsMapSerializer::{serialize_seq,serialize_map}` -\u003e `Vec::with_capacity(len - 1)` or `Vec::with_capacity(len.unwrap_or(17) - 1)` -\u003e 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\u003cString\u003e);\n\n#[serde_as]\n#[derive(Serialize)]\n#[serde(transparent)]\nstruct KVMap {\n #[serde_as(as = \"KeyValueMap\u003c_\u003e\")]\n foo: Vec\u003cSeq\u003e,\n}\n\nfn main() {\n let value = KVMap {\n foo: vec![Seq(Vec::new())],\n };\n let _ = serde_json::to_string(\u0026value).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.",
"id": "GHSA-7gcf-g7xr-8hxj",
"modified": "2026-08-31T14:18:13Z",
"published": "2026-07-15T22:41:01Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"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",
"type": "CVSS_V4"
}
],
"summary": "serde_with: KeyValueMap serialization panics on empty sequence or map entries"
}
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