GHSA-7GCF-G7XR-8HXJ
Vulnerability from github – Published: 2026-07-15 22:41 – Updated: 2026-07-15 22:41
VLAI
Summary
serde_with: KeyValueMap serialization panics on empty sequence or map entries
Details
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 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.
Severity
{
"affected": [
{
"package": {
"ecosystem": "crates.io",
"name": "serde_with"
},
"ranges": [
{
"events": [
{
"introduced": "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": "2026-07-15T22:41:01Z",
"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/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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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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