diff --git a/src/agent/src/image_rpc.rs b/src/agent/src/image_rpc.rs
index 298b79b7bf..1176735351 100644
--- a/src/agent/src/image_rpc.rs
+++ b/src/agent/src/image_rpc.rs
@@ -203,6 +203,24 @@ impl ImageService {
         Ok(())
     }
 
+    /// Determines the container id (cid) to use for a given request.
+    ///
+    /// If the request specifies a non-empty id, use it; otherwise derive it from the image path.
+    /// In either case, verify that the chosen id is valid.
+    fn cid_from_request(req: &image::PullImageRequest) -> Result<String> {
+        let req_cid = req.get_container_id();
+        let cid = if !req_cid.is_empty() {
+            req_cid.to_string()
+        } else if let Some(last) = req.get_image().rsplit('/').next() {
+            // ':' have special meaning for umoci during upack
+            last.replace(':', "_")
+        } else {
+            return Err(anyhow!("Invalid image name. {}", req.get_image()));
+        };
+        verify_cid(&cid)?;
+        Ok(cid)
+    }
+
     async fn pull_image(&self, req: &image::PullImageRequest) -> Result<String> {
         env::set_var("OCICRYPT_KEYPROVIDER_CONFIG", OCICRYPT_CONFIG_PATH);
 
@@ -216,33 +234,19 @@ impl ImageService {
             env::set_var("NO_PROXY", no_proxy);
         }
 
+        let cid = Self::cid_from_request(req)?;
         let image = req.get_image();
-        let mut cid = req.get_container_id().to_string();
-
-        let aa_kbc_params = &AGENT_CONFIG.read().await.aa_kbc_params;
-
-        if cid.is_empty() {
-            let v: Vec<&str> = image.rsplit('/').collect();
-            if !v[0].is_empty() {
-                // ':' have special meaning for umoci during upack
-                cid = v[0].replace(':', "_");
-            } else {
-                return Err(anyhow!("Invalid image name. {}", image));
-            }
-        } else {
-            verify_cid(&cid)?;
-        }
-
         // Can switch to use cid directly when we remove umoci
         let v: Vec<&str> = image.rsplit('/').collect();
         if !v[0].is_empty() && v[0].starts_with("pause:") {
             Self::unpack_pause_image(&cid)?;
 
             let mut sandbox = self.sandbox.lock().await;
-            sandbox.images.insert(String::from(image), cid.to_string());
+            sandbox.images.insert(String::from(image), cid);
             return Ok(image.to_owned());
         }
 
+        let aa_kbc_params = &AGENT_CONFIG.read().await.aa_kbc_params;
         if !aa_kbc_params.is_empty() {
             match self.attestation_agent_started.compare_exchange_weak(
                 false,
@@ -288,7 +292,7 @@ impl ImageService {
         }
 
         let mut sandbox = self.sandbox.lock().await;
-        sandbox.images.insert(String::from(image), cid.to_string());
+        sandbox.images.insert(String::from(image), cid);
         Ok(image.to_owned())
     }
 }
@@ -312,3 +316,96 @@ impl protocols::image_ttrpc_async::Image for ImageService {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::ImageService;
+    use protocols::image;
+
+    #[test]
+    fn test_cid_from_request() {
+        struct Case {
+            cid: &'static str,
+            image: &'static str,
+            result: Option<&'static str>,
+        }
+
+        let cases = [
+            Case {
+                cid: "",
+                image: "",
+                result: None,
+            },
+            Case {
+                cid: "..",
+                image: "",
+                result: None,
+            },
+            Case {
+                cid: "",
+                image: "..",
+                result: None,
+            },
+            Case {
+                cid: "",
+                image: "abc/..",
+                result: None,
+            },
+            Case {
+                cid: "",
+                image: "abc/",
+                result: None,
+            },
+            Case {
+                cid: "",
+                image: "../abc",
+                result: Some("abc"),
+            },
+            Case {
+                cid: "",
+                image: "../9abc",
+                result: Some("9abc"),
+            },
+            Case {
+                cid: "some-string.1_2",
+                image: "",
+                result: Some("some-string.1_2"),
+            },
+            Case {
+                cid: "0some-string.1_2",
+                image: "",
+                result: Some("0some-string.1_2"),
+            },
+            Case {
+                cid: "a:b",
+                image: "",
+                result: None,
+            },
+            Case {
+                cid: "",
+                image: "prefix/a:b",
+                result: Some("a_b"),
+            },
+            Case {
+                cid: "",
+                image: "/a/b/c/d:e",
+                result: Some("d_e"),
+            },
+        ];
+
+        for case in &cases {
+            let mut req = image::PullImageRequest::new();
+            req.set_image(case.image.to_string());
+            req.set_container_id(case.cid.to_string());
+            let ret = ImageService::cid_from_request(&req);
+            match (case.result, ret) {
+                (Some(expected), Ok(actual)) => assert_eq!(expected, actual),
+                (None, Err(_)) => (),
+                (None, Ok(r)) => panic!("Expected an error, got {}", r),
+                (Some(expected), Err(e)) => {
+                    panic!("Expected {} but got an error ({})", expected, e)
+                }
+            }
+        }
+    }
+}