diff --git a/libafl/src/executors/command.rs b/libafl/src/executors/command.rs
index 4158250532..85640876bd 100644
--- a/libafl/src/executors/command.rs
+++ b/libafl/src/executors/command.rs
@@ -1,5 +1,5 @@
 //! The command executor executes a sub program for each run
-use alloc::{string::String, vec::Vec};
+use alloc::vec::Vec;
 use core::{
     fmt::{self, Debug, Formatter},
     marker::PhantomData,
@@ -335,21 +335,21 @@ where
         };
 
         if self.observers.observes_stderr() {
-            let mut stderr = String::new();
+            let mut stderr = Vec::new();
             child.stderr.as_mut().ok_or_else(|| {
                 Error::illegal_state(
                     "Observer tries to read stderr, but stderr was not `Stdio::pipe` in CommandExecutor",
                 )
-            })?.read_to_string(&mut stderr)?;
+            })?.read_to_end(&mut stderr)?;
             self.observers.observe_stderr(&stderr);
         }
         if self.observers.observes_stdout() {
-            let mut stdout = String::new();
+            let mut stdout = Vec::new();
             child.stdout.as_mut().ok_or_else(|| {
                 Error::illegal_state(
                     "Observer tries to read stdout, but stdout was not `Stdio::pipe` in CommandExecutor",
                 )
-            })?.read_to_string(&mut stdout)?;
+            })?.read_to_end(&mut stdout)?;
             self.observers.observe_stdout(&stdout);
         }
 
diff --git a/libafl/src/executors/differential.rs b/libafl/src/executors/differential.rs
index 4e24b4d114..f8d2c70143 100644
--- a/libafl/src/executors/differential.rs
+++ b/libafl/src/executors/differential.rs
@@ -151,13 +151,13 @@ where
     }
 
     /// Runs `observe_stdout` for all stdout observers in the list
-    fn observe_stdout(&mut self, stdout: &str) {
+    fn observe_stdout(&mut self, stdout: &[u8]) {
         self.primary.as_mut().observe_stderr(stdout);
         self.secondary.as_mut().observe_stderr(stdout);
     }
 
     /// Runs `observe_stderr` for all stderr observers in the list
-    fn observe_stderr(&mut self, stderr: &str) {
+    fn observe_stderr(&mut self, stderr: &[u8]) {
         self.primary.as_mut().observe_stderr(stderr);
         self.secondary.as_mut().observe_stderr(stderr);
     }
diff --git a/libafl/src/observers/mod.rs b/libafl/src/observers/mod.rs
index 8702187c64..5920fbe1ce 100644
--- a/libafl/src/observers/mod.rs
+++ b/libafl/src/observers/mod.rs
@@ -106,13 +106,13 @@ where
     /// To use this, always return `true` from `observes_stdout`
     #[inline]
     #[allow(unused_variables)]
-    fn observe_stdout(&mut self, stdout: &str) {}
+    fn observe_stdout(&mut self, stdout: &[u8]) {}
 
     /// React to new `stderr`
     /// To use this, always return `true` from `observes_stderr`
     #[inline]
     #[allow(unused_variables)]
-    fn observe_stderr(&mut self, stderr: &str) {}
+    fn observe_stderr(&mut self, stderr: &[u8]) {}
 }
 
 /// Defines the observer type shared across traits of the type.
@@ -155,9 +155,9 @@ where
     fn observes_stderr(&self) -> bool;
 
     /// Runs `observe_stdout` for all stdout observers in the list
-    fn observe_stdout(&mut self, stdout: &str);
+    fn observe_stdout(&mut self, stdout: &[u8]);
     /// Runs `observe_stderr` for all stderr observers in the list
-    fn observe_stderr(&mut self, stderr: &str);
+    fn observe_stderr(&mut self, stderr: &[u8]);
 }
 
 impl<S> ObserversTuple<S> for ()
@@ -205,12 +205,12 @@ where
     /// Runs `observe_stdout` for all stdout observers in the list
     #[inline]
     #[allow(unused_variables)]
-    fn observe_stdout(&mut self, stdout: &str) {}
+    fn observe_stdout(&mut self, stdout: &[u8]) {}
 
     /// Runs `observe_stderr` for all stderr observers in the list
     #[inline]
     #[allow(unused_variables)]
-    fn observe_stderr(&mut self, stderr: &str) {}
+    fn observe_stderr(&mut self, stderr: &[u8]) {}
 }
 
 impl<Head, Tail, S> ObserversTuple<S> for (Head, Tail)
@@ -263,14 +263,14 @@ where
 
     /// Runs `observe_stdout` for all stdout observers in the list
     #[inline]
-    fn observe_stdout(&mut self, stdout: &str) {
+    fn observe_stdout(&mut self, stdout: &[u8]) {
         self.0.observe_stdout(stdout);
         self.1.observe_stdout(stdout);
     }
 
     /// Runs `observe_stderr` for all stderr observers in the list
     #[inline]
-    fn observe_stderr(&mut self, stderr: &str) {
+    fn observe_stderr(&mut self, stderr: &[u8]) {
         self.0.observe_stderr(stderr);
         self.1.observe_stderr(stderr);
     }
@@ -991,10 +991,10 @@ pub mod pybind {
         }
 
         #[inline]
-        fn observe_stderr(&mut self, _: &str) {}
+        fn observe_stderr(&mut self, _: &[u8]) {}
 
         #[inline]
-        fn observe_stdout(&mut self, _: &str) {}
+        fn observe_stdout(&mut self, _: &[u8]) {}
     }
 
     impl MatchName for PythonObserversTuple {
diff --git a/libafl/src/observers/stacktrace.rs b/libafl/src/observers/stacktrace.rs
index e228b38880..5571988895 100644
--- a/libafl/src/observers/stacktrace.rs
+++ b/libafl/src/observers/stacktrace.rs
@@ -269,8 +269,8 @@ where
     }
 
     /// Do nothing on new `stderr`
-    fn observe_stderr(&mut self, stderr: &str) {
-        self.parse_asan_output(stderr);
+    fn observe_stderr(&mut self, stderr: &[u8]) {
+        self.parse_asan_output(&String::from_utf8_lossy(stderr));
     }
 }
 
diff --git a/libafl/src/observers/stdio.rs b/libafl/src/observers/stdio.rs
index ca046781aa..6f585b1abc 100644
--- a/libafl/src/observers/stdio.rs
+++ b/libafl/src/observers/stdio.rs
@@ -3,6 +3,7 @@
 //! For example, they are supported on the [`crate::executors::CommandExecutor`].
 
 use alloc::string::String;
+use std::vec::Vec;
 
 use serde::{Deserialize, Serialize};
 
@@ -15,7 +16,7 @@ pub struct StdOutObserver {
     /// The name of the observer.
     pub name: String,
     /// The stdout of the target during its last execution.
-    pub stdout: Option<String>,
+    pub stdout: Option<Vec<u8>>,
 }
 
 /// An observer that captures stdout of a target.
@@ -37,7 +38,7 @@ where
     }
 
     /// React to new `stdout`
-    fn observe_stdout(&mut self, stdout: &str) {
+    fn observe_stdout(&mut self, stdout: &[u8]) {
         self.stdout = Some(stdout.into());
     }
 }
@@ -55,7 +56,7 @@ pub struct StdErrObserver {
     /// The name of the observer.
     pub name: String,
     /// The stderr of the target during its last execution.
-    pub stderr: Option<String>,
+    pub stderr: Option<Vec<u8>>,
 }
 
 /// An observer that captures stderr of a target.
@@ -77,7 +78,7 @@ where
     }
 
     /// React to new `stderr`
-    fn observe_stderr(&mut self, stderr: &str) {
+    fn observe_stderr(&mut self, stderr: &[u8]) {
         self.stderr = Some(stderr.into());
     }
 }