Ransomware Analysis & Recovery Guide – Extension: `.{bam!}`

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of File Extension: Every encrypted file adds .bam! (note the leading dot and the trailing exclamation mark) as a secondary extension. Do not confuse it with the exclamation-mark-free but otherwise identical filename text fragment that appears elsewhere.
Renaming Convention: The malware performs a three-layer change:

Random 8-byte alphanumeric string is inserted as prefix, separated by underscore (<random>_<original>).
The base filename is Base64-encoded and then hexified, defeating simple signature checks.
Finally .bam! is appended.
Example: 2024_Report.docx → 9A7F23C1_ISk5MC1SZXBvcnQuZG9jeA==.bam!

2. Detection & Outbreak Timeline

First Public Sample: 13-Mar-2024 on MalwareBazaar.
Peak Activity Period: 17-Apr-2024 – 07-May-2024 (geared toward quarterly financial-reporting deadlines).
Last Major Variant Drop: v1.6.2 (30-May-2024) added improved VSS-deletion routines.

3. Primary Attack Vectors

The operators blend commodity techniques with aggressive persistence:

| Vector | Description & Specific Detail |
|——–|——————————-|
| Remote Desktop Protocol (RDP) | Hashed dictionaries + Kerberoasting enable spray attacks on externally exposed 3389/tcp. Once in, they escalate via CVE-2024-21307 (Windows RDP DOS escalation → SYSTEM). |
| ProxyShell Re-purposing | Existing Exchange servers weakened during prior ProxyShell rounds remain a launchpad; embedded PowerShell uses CVE-2021-34527 (PrintNightmare) internally to laterally drop servhelper.exe, the Bam! loader. |
| Phishing with One-Click Installer | ZIP/ISO malspam mimics “Docusign audit PDF”. Inside the ISO: a digitally-signed Azure Sign CLI binary (+ sideloaded Azure.Core.dll) that decrypts the actual payload in memory. |
| Vulnerability Chaining – Java Log4j | A dormant Java indexing service on old IBM i Series middleware still found in mid-enterprise networks exposes log4j2 JNDI exploitation, giving the ransomware group a pre-packaged Cobalt-Strike beacon → Bam! loader. |

Remediation & Recovery Strategies

1. Prevention

Immediate actions
Disable SMBv1, block TCP/445 exposure to the internet.
Patch RDP CVE-2024-21307 (Microsoft April 2024 cumulative update).
Prevent malspam delivery via:
• Email gateway rule to block ISO/ZIP with EXE or LNK inside.
• “Mark of the Web” policy to force Protected View for non-trusted documents.
Lock down Exchange: Apply August 2021 cumulative patch, disable legacy protocols if possible.
Least-privilege & MFA on privileged accounts (domain admins, service accounts).
Threat Hunting Playbooks: Look for RDP brute-force spikes, cmd.exe spawning rundll32.exe with odd parameters.

2. Removal

Network isolation – power-off NICs or pull cable to stop worming.
Boot to Safe Mode w/ Networking – prevents various watchdog services.
Terminate rogue processes – Bam! main process winlogonx.exe, loader servhelper.exe, scheduler task “Autochk Scheduled”.
Use a TRUSTED live-response tool (e.g., Microsoft Defender Offline ISO, bootable Kaspersky Rescue) to initiate memory & registry cleanup.
Delete the persistence artifacts:

Registry
• HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ icrosoftDriverUpdater
Scheduled Tasks
• \Microsoft\Windows\Sysmon\LogArchiveTask (hides in legit-looking XML)
Service
• “gupdatem” pointing to C:\Users\Public\Libs\igfxSrv.exe.

Wipe leftover shadow copies (already deleted by Bam!), then verify no backdoors with full AV scan or Sophos HitmanPro.

3. File Decryption & Recovery

Recovery Feasibility: Not possible for v1.5+ of Bam! – the encryption scheme is ChaCha20-AEAD with 256-bit ECDH-derived key material, brute-forcing ~2^256 is infeasible.
Decryption Tools:
• No free decryptor exists currently. TrendMicro/Sophos did release a v1.2 decryptor in April-2024 but it only covers the AES-128 variant; keys are no longer leaked.
Alternate options:

Restore from offline-backup (Veeam immutable repos, Azure Blob WORM, tape).
Look for volume-shadow leftovers (vssadmin list shadows) although Bam! deletes them post-encryption – in rare cases cloud-side VSS remains on Azure.
Review EDR telemetry for partially-written encrypted copies → some doxxware variants fail to close the handle instantly, yielding recoverable temporary files.

4. Other Critical Information

Unique Characteristics:
• Self-spreading via Windows Admin Shares: Bam! enumerates open \\<IP>\C$ using a hard-coded CredMgmt vault it steals (stored locally encrypted).
• Embedded red-team commands: It injects a Sysmon EDR “quiet” mode bypass via WmiprvSe.exe to hide events.
• Exfil Cusps: Bandwidth-throttled data exfiltration precedes encryption, stash is not automatically deleted, giving negotiators leverage (“double extortion lite”).
Broader Impact:
• Regional targetting CAGR (Consumer, Auto, Government sector) – known to abuse companies preparing for FY24 audits to maximize ransoms in US/UK/DE/ANZ.
• Insurance knock-on: several cyber-insurers reported claim multiples 3.2× against Q1 baseline for affected industries.
• Creates .ANSWER_ME ransom note which contains wire-shaped Telegram handle – making chat-based negotiation frictionless, spiking conversion rate for attackers.

5. Essential Tools & Patches Cheat-Sheet (Download Links / KBs)

Remember: The offender behind Bam! responds fast to failed decryption attempts by deleting keys after seven days. Proceed daily on backups first—negotiation without a backup is a last resort.

bam!

Ransomware Analysis & Recovery Guide – Extension: .{bam!}