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Response snapshot Oct 27, 2026, 16:01 UTC

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VulnerabilityGHSA-3w55-933p-8pv5

Strands Agents: Local Privilege Escalation via Symlink Attack in Default Session File Storage

The `FileSessionManager` defaults to storing session data in `/tmp/strands/sessions/` (a world-writable directory) using predictable file paths and a write pattern (`open(path + ".tmp", "w")` → `os.replace()`) that follows symbolic links.

Published Updated

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: strands-agents: 1.48.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-3w55-933p-8pv5 (opens a new tab)

What happened

## Summary

The `FileSessionManager` defaults to storing session data in `/tmp/strands/sessions/` (a world-writable directory) using predictable file paths and a write pattern (`open(path + ".tmp", "w")` → `os.replace()`) that follows symbolic links. A local attacker can exploit this to overwrite arbitrary files or inject malicious session data for persistent prompt injection.

## Vulnerability Details

**Component:** `strands-py/src/strands/session/file_session_manager.py`

Continue reading

**Root Cause:** 1. Default storage directory is `tempfile.gettempdir() + "/strands/sessions/"` (line 58) — resolves to `/tmp/strands/sessions/` on Linux/macOS 2. The `_write_file()` method (lines 116-123) writes to a predictable `.tmp` path without symlink protection: ```python tmp = f"{path}.tmp" with open(tmp, "w", encoding="utf-8", newline="\n") as f: json.dump(data, f, indent=2, ensure_ascii=False) os.

replace(tmp, path) ``` 3. `open()` follows symlinks — a pre-placed symlink at the `.tmp` path causes writes to an arbitrary target file 4. No integrity verification (HMAC/signature) on session files — tampered data is loaded as-is

## Attack Vectors

### 1. Arbitrary File Overwrite (Local Privilege Escalation) 1. Attacker pre-creates `/tmp/strands/sessions/session_ /` (or monitors for new directories via inotify) 2. Attacker creates a symlink: `session.json.tmp` → `/home/victim/.bashrc` (or any writable file) 3. Victim application writes session data → follows symlink → overwrites target file with JSON content 4. Attacker achieves code execution on next shell login (or targets `.ssh/authorized_keys`, cron files, etc.)

### 2. Persistent Prompt Injection via Session Tampering 1. Attacker writes crafted message files into the session directory 2. Victim application restores the session → loads attacker-controlled conversation history 3. Injected messages instruct the agent to execute attacker commands on every future interaction 4. No integrity check prevents this — the SDK trusts all session files at face value

## Impact

- **Arbitrary file overwrite** — local attacker can write attacker-controlled content to any file writable by the victim process - **Local privilege escalation** — via overwriting shell configs, SSH keys, cron jobs, or systemd user services - **Persistent agent compromise** — via session data injection, the agent follows attacker instructions indefinitely

## Reproduction

```python import os, json, tempfile, shutil

# Setup: simulate the vulnerable write pattern session_dir = "/tmp/strands/sessions/session_test/" os.makedirs(session_dir, exist_ok=True)

# Attacker: create symlink at the .tmp write path target_file = "/tmp/symlink_attack_proof.txt" with open(target_file, "w") as f: f.write("ORIGINAL - should not be overwritten\n")

symlink_path = os.path.join(session_dir, "session.json.tmp") if os.path.exists(symlink_path): os.unlink(symlink_path) os.symlink(target_file, symlink_path)

# Victim: FileSessionManager._write_file() equivalent with open(symlink_path, "w", encoding="utf-8", newline="\n") as f: json.dump({"session_id": "test", "injected": True}, f, indent=2)

# Verify: target file overwritten with open(target_file) as f: print(f"Target file content: {f.read()}") # Output: {"session_id": "test", "injected": true}

# Cleanup os.unlink(symlink_path) os.unlink(target_file) shutil.rmtree(session_dir) ```

## Suggested Fix

1. **Use a user-private default directory** — `~/.strands/sessions/` or `$XDG_DATA_HOME/strands/sessions/` instead of `/tmp/` 2. **Use `os.open()` with `O_NOFOLLOW | O_CREAT | O_WRONLY`** — refuses to follow symlinks 3. **Use `tempfile.mkstemp()`** for atomic writes instead of predictable `.tmp` suffix 4. **Verify directory ownership** matches the current user before writing 5. **Add optional integrity verification** (HMAC) on session files to detect tampering

Affected package ranges reported by GitHub: strands-agents: < 1.48.0

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-3w55-933p-8pv5 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-3w55-933p-8pv5, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). Strands Agents: Local Privilege Escalation via Symlink Attack in Default Session File Storage. https://kevwire.com/record/GHSA-3w55-933p-8pv5

MLA

"Strands Agents: Local Privilege Escalation via Symlink Attack in Default Session File Storage." KEVWire, 27 Oct. 2026, kevwire.com/record/GHSA-3w55-933p-8pv5.

Chicago

KEVWire. "Strands Agents: Local Privilege Escalation via Symlink Attack in Default Session File Storage." Last modified October 27, 2026. https://kevwire.com/record/GHSA-3w55-933p-8pv5.

Evidence summary (plain text)

Strands Agents: Local Privilege Escalation via Symlink Attack in Default Session File Storage (Oct 27, 2026).
The `FileSessionManager` defaults to storing session data in `/tmp/strands/sessions/` (a world-writable directory) using predictable file paths and a write pattern (`open(path + ".tmp", "w")` → `os.replace()`) that follows symbolic links. A local attacker can exploit this to overwrite arbitrary files or inject malicious session data for persistent prompt injection.

**Component:** `strands-py/src/strands/session/file_session_manager.py`
Sources:
GitHub-reviewed advisory GHSA-3w55-933p-8pv5: https://github.com/advisories/GHSA-3w55-933p-8pv5
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-3w55-933p-8pv5.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 16:00 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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