Add unmaintained libyml and serde_yml

HOWTO_UNMAINTAINED.md

@@ -71,6 +71,10 @@ When creating the advisory, please include a link to an open issue
 on the upstream project repository where the maintenance status has been
 discussed in the `url = "..."` field of the advisory.
 
+If the upstream project repository has issues disabled, or if an upstream
+issue does not adequately explain the circumstances, please include
+`url = "..."` linking to an issue in the `advisory-db` project.
+
 For more information on adding an advisory to the RustSec DB, see:
 
 <https://github.com/RustSec/advisory-db/blob/main/CONTRIBUTING.md>

crates/libyml/RUSTSEC-0000-0000.md

@@ -0,0 +1,21 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "libyml"
+date = "2025-09-11"
+url = "https://github.com/rustsec/advisory-db/issues/2395"
+informational = "unmaintained"
+
+[versions]
+patched = []
+```
+
+# libyml crate is unmaintained
+
+The `libyml` crate is no longer actively maintained.
+If you rely on this crate, it is highly recommended switching to a maintained alternative.
+
+## Recommended alternatives
+
+- [`libyaml-safer`](https://crates.io/crates/libyaml-safer) 
+- [`unsafe-libyaml-norway`](https://crates.io/crates/unsafe-libyaml-norway) - Maintained fork of `unsafe-libyaml`

crates/serde_yml/RUSTSEC-0000-0000.md

@@ -0,0 +1,26 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "serde_yml"
+date = "2025-09-11"
+url = "https://github.com/rustsec/advisory-db/issues/2395"
+informational = "unmaintained"
+
+[versions]
+patched = []
+```
+
+# serde_yml crate is unmaintained
+
+The `serde_yml` crate is no longer actively maintained, after unsounded issues were raised.
+If you rely on this crate, it is highly recommended switching to a maintained alternative.
+
+## Recommended alternatives
+
+- [`serde_norway`](https://crates.io/crates/serde_norway) - Maintained fork of `serde_yaml`, using `unsafe-libyaml-norway`
+- [`serde_yaml_ng`](https://crates.io/crates/serde_yaml_ng) - Maintained fork of `serde_yaml`, using unmaintained `unsafe-libyaml`
+
+## Incomplete alternatives
+
+- [`serde_yaml2`](https://crates.io/crates/serde_yaml2)
+- [`yaml-peg`](https://crates.io/crates/yaml-peg)