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+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "cgmath"
+date = "2026-03-11"
+url = "https://github.com/rustgd/cgmath/issues/565"
+informational = "unsound"
+categories = ["memory-corruption"]
+keywords = ["soundness", "undefined-behavior", "aliasing", "stacked-borrows"]
+
+[affected.functions]
+"cgmath::Matrix2::swap_columns" = ["= 0.18.0"]
+"cgmath::Matrix3::swap_columns" = ["= 0.18.0"]
+"cgmath::Matrix4::swap_columns" = ["= 0.18.0"]
+
+[versions]
+patched = []
+```
+
+# `Matrix{2,3,4}::swap_columns` can trigger undefined behavior for identical indices
+
+The `Matrix2::swap_columns`, `Matrix3::swap_columns`, and `Matrix4::swap_columns`
+implementations call `ptr::swap(&mut self[a], &mut self[b])`.
+
+When `a == b`, these safe APIs create two mutable references to the same matrix
+column and pass them to `ptr::swap`. This violates Rust's aliasing rules and can
+trigger undefined behavior. The issue can be reproduced from safe Rust by calling
+`swap_columns` with identical column indices, for example `m.swap_columns(0, 0)`.
+
+## Example
+
+The issue can be triggered without unsafe code in the caller:
+
+```rust
+use cgmath::{Matrix, Matrix2};
+
+fn main() {
+    let mut m = Matrix2::new(1.0, 2.0, 3.0, 4.0);
+    m.swap_columns(0, 0);
+}
+```
+
+```rust
+use cgmath::{Matrix, Matrix3};
+
+fn main() {
+    let mut m = Matrix3::new(
+        1.0, 2.0, 3.0,
+        4.0, 5.0, 6.0,
+        7.0, 8.0, 9.0,
+    );
+    m.swap_columns(1, 1);
+}
+```
+
+```rust
+use cgmath::{Matrix, Matrix4};
+
+fn main() {
+    let mut m = Matrix4::new(
+        1.0, 2.0, 3.0, 4.0,
+        5.0, 6.0, 7.0, 8.0,
+        9.0, 10.0, 11.0, 12.0,
+        13.0, 14.0, 15.0, 16.0,
+    );
+    m.swap_columns(2, 2);
+}
+```
+
+## Miri output
+
+The issue was validated with Miri on `cgmath` 0.18.0. For the `Matrix2`
+reproducer, Miri reports:
+
+```text
+error: Undefined Behavior: attempting a read access using <281> at alloc120[0x0],
+but that tag does not exist in the borrow stack for this location
+   --> core/src/ptr/mod.rs:1308:9
+    |
+1308 |         copy_nonoverlapping(x, tmp.as_mut_ptr(), 1);
+    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    = note: inside `std::ptr::swap::<cgmath::Vector2<f64>>`
+    = note: inside `<cgmath::Matrix2<f64> as cgmath::Matrix>::swap_columns`
+note: inside `main`
+   --> src/main.rs:9:5
+    |
+9   |     m.swap_columns(0, 0);
+    |     ^^^^^^^^^^^^^^^^^^^^
+```
+
+The `Matrix3` and `Matrix4` reproducers produce the same class of Stacked
+Borrows violation, with the backtrace pointing to their corresponding
+`swap_columns` implementations.
+
+A minimal fix is to return early when the two column indices are equal before
+calling `ptr::swap`.