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Response snapshot Oct 27, 2026, 05:12 UTC

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VulnerabilityCVE-2026-107839

ageLANServer: Unbounded JSON Array Allocation in AoE3 Cloud `getFileURL` Endpoint Leads to Remote Denial of Service

```go type getFileURLRequest struct { Names i.Json[[]string] `json:"names"` } func GetFileURL(w http.ResponseWriter, r *http.Request) { var req getFileURLRequest err := i.Bind(r, &req) ... descriptions := make(i.A, len(req.Names.Data)) for j, name := range req.Names.Data { ... ```

Published Updated

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.4% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: github.com/luskaner/ageLANServer/server: 1.8.2-0.20260809203301-1dd40166a593. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-4jfq-pmq9-257h (opens a new tab)

What happened

### Summary The AoE3 `POST /game/cloud/getFileURL` handler in `luskaner/ageLANServer`'s bundled game server decodes an attacker-controlled `names` JSON array and immediately allocates response storage sized directly from the array's length (`make(i.A, len(req.Names.Data))`), with no request body size limit and no cap on the number of array elements anywhere in the request path.

Because the default configuration ships with `Authentication = 'disabled'`, any network client can obtain a session through unauthenticated platform login and then send a single crafted request that forces the server to allocate memory proportional to attacker-chosen input.

Dynamic testing against an unmodified build confirmed both large memory-amplification growth from a single request and a full server process kill via the kernel OOM killer when a memory-constrained instance received a few concurrent oversized requests. This is a high-severity, pre-authentication (self-registration only) remote denial-of-service vulnerability (CVSS 3.1 Base Score 7.5, CWE-400).

### Details `server/internal/routes/game/cloud/getFileURL.go` defines the request struct and handler for the AoE3 cloud "get file URL" endpoint:

Continue reading

```go type getFileURLRequest struct { Names i.Json[[]string] `json:"names"` }

func GetFileURL(w http.ResponseWriter, r *http.Request) { var req getFileURLRequest err := i.Bind(r, &req) ... descriptions := make(i.A, len(req.Names.Data)) for j, name := range req.Names.Data { ... ```

`Names` is typed as `i.Json[[]string]`, a wrapper whose `UnmarshalText` is invoked by `encoding/json` whenever the incoming JSON value for `names` is itself a string, so the attacker supplies a JSON-string-encoded array (e.g. `{"names":"[\"x\",\"x\",...]"}`). The request body is decoded in `server/internal/http.go`'s `Bind()` via `json.NewDecoder(r.Body).Decode(data)`, with no `http.

MaxBytesReader`, no `LimitReader`, and no `MaxHeaderBytes` configured on the `http.Server` in `server/internal/cmd/root.go`. There is also no branch-neutral cap on `len(req.Names.Data)` — the same unbounded length is also used at `getFileURL.go:27` (`slices.Repeat(i.A{nil}, len(req.Names.Data))` when the cloud file cache is empty) in addition to the `make(i.A, len(req.Names.Data))` sink at line 30.

Because `len()` on the attacker-supplied slice is used directly as an allocation size with no upper bound, an attacker can force the server to allocate memory (and CPU cycles decoding/iterating) proportional to the size of a single HTTP request body, which is itself unbounded.

Reaching this code path requires only a valid session, not real game ownership or credentials: - The endpoint is registered for the AoE3 title at `server/internal/routes/router/game.go:267`. - `server/internal/routes/router/sessionMiddleware.go:23-36` only checks that `sessionID` resolves to an existing session — it performs no additional authorization. - The default configuration `server/resources/config/config.

toml` sets `Authentication = 'disabled'`. Combined with `server/internal/routes/game/login/platformlogin.go`, which issues a session for any client-supplied `accountType`/`platformUserID` without verifying it against a real platform, an attacker can obtain a valid `sessionID` with a single unauthenticated `platformlogin` request and no prior credentials.

Data flow (source → sink): 1. `server/resources/unix/start_age3.sh:4` (or `start_age3.bat`) starts the release server with `-e age3`, the default supported way to run the AoE3 server. 2. `server/internal/routes/router/game.go:267` registers `POST /game/cloud/getFileURL`. 3. `server/internal/routes/router/sessionMiddleware.go:23-36` accepts any request bearing a valid `sessionID`. 4. `server/internal/http.

go` decodes the JSON body into `getFileURLRequest` with no size limiting. 5. `server/internal/routes/game/cloud/getFileURL.go:13-19` binds the attacker-controlled `names` array into `req.Names`. 6. `server/internal/routes/game/cloud/getFileURL.go:27` and `:30` allocate slices sized directly by `len(req.Names.Data)`.

### PoC Environment: Docker (see `Dockerfile`), which builds the **unmodified** `server` and `genCert` binaries directly from the repository source at commit `405b9a9` (equivalent to the previously reported `870b90c`) and starts the AoE3 server (`./server -e age3`) with the shipped default configuration (`Authentication = 'disabled'`), only disabling LAN announcement broadcast since it is irrelevant to the sandboxed reproduction.

Build and run: ```bash docker build -f vuln-001/Dockerfile -t agelan-vuln001 repo docker run -d --name agelan-vuln001-test -p 8443:443 --memory=300m agelan-vuln001 ```

Attack script: `poc.py` (see file for full source). At a high level it: 1. Calls `POST /game/login/platformlogin` with an arbitrary Steam-style `accountType`/`platformUserID`/`macAddress` to obtain a session id, exploiting the default `Authentication = 'disabled'` setting. 2. Sends a small baseline `POST /game/cloud/getFileURL?

sessionID= ` request (`names` array with 5 elements) and records server RSS before/after via `docker exec ... cat /proc/1/status`. 3. Sends a single request with `names` containing 2,000,000 elements and records the resulting RSS growth relative to request size (memory amplification). 4.

Against the same container restarted with `--memory=300m`, fires 3 concurrent requests each with `names` containing 3,000,000 elements, then inspects `docker inspect` state to check for an OOM kill.

```bash python3 poc.py --host 127.0.0.1 --port 8443 --container agelan-vuln001-test ```

Observed results (Phase 2 dynamic reproduction, unmodified source): - Baseline request (`names` count = 5, 43 request bytes): server RSS unchanged (16928 KB → 16928 KB). - Single moderately large request (`names` count = 2,000,000, 12,000,013 request bytes): server RSS jumped from 16,984 KB to 224,724 KB — a growth of 207,740 KB from a ~11.4 MB request (~17.73x amplification of request size in RSS growth). - Concurrent attack

Affected package ranges reported by GitHub: github.com/luskaner/ageLANServer/server: < 1.8.2-0.20260809203301-1dd40166a593

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.4%

Scored Percentile 35.5%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-4jfq-pmq9-257h (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-4jfq-pmq9-257h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-107839, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 22). ageLANServer: Unbounded JSON Array Allocation in AoE3 Cloud `getFileURL` Endpoint Leads to Remote Denial of Service (CVE-2026-107839). https://kevwire.com/record/CVE-2026-107839

MLA

"ageLANServer: Unbounded JSON Array Allocation in AoE3 Cloud `getFileURL` Endpoint Leads to Remote Denial of Service (CVE-2026-107839)." KEVWire, 22 Oct. 2026, kevwire.com/record/CVE-2026-107839.

Chicago

KEVWire. "ageLANServer: Unbounded JSON Array Allocation in AoE3 Cloud `getFileURL` Endpoint Leads to Remote Denial of Service (CVE-2026-107839)." Last modified October 22, 2026. https://kevwire.com/record/CVE-2026-107839.

Evidence summary (plain text)

ageLANServer: Unbounded JSON Array Allocation in AoE3 Cloud `getFileURL` Endpoint Leads to Remote Denial of Service (Oct 9, 2026).
```go
type getFileURLRequest struct {
 Names i.Json[[]string] `json:"names"`
}

func GetFileURL(w http.ResponseWriter, r *http.Request) {
 var req getFileURLRequest
 err := i.Bind(r, &req)
 ...
 descriptions := make(i.A, len(req.Names.Data))
 for j, name := range req.Names.Data {
 ...
```
CVSS 7.5 (version 3.1; evidence as of Oct 22, 2026; https://github.com/advisories/GHSA-4jfq-pmq9-257h).
EPSS 0.4% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-107839&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-4jfq-pmq9-257h: https://github.com/advisories/GHSA-4jfq-pmq9-257h
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNTo1Mjo1NlrOAAfxiA%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNDowNjoxNFrOAAfxZw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQwODoyNzoyM1rOAAYp9A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTozNlrOAAf0Jw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTowNVrOAAf0JQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0Mzo0NVrOAAf0Iw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0MzozMVrOAAf0Ig%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozNTowMVrOAAZRcw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozMDoyN1rOAAY_5Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODoyOTowNVrOAAfz8g%3D%3D
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-107839&date=2026-10-26
Record ID: CVE-2026-107839.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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