CVE-2026-68768 Overview
CVE-2026-68768 is a heap-based buffer overflow ([CWE-120]) in the outfile_write() function within src/outfile.c of the hashcat password recovery tool. The function assembles output into a fixed HCBUFSIZ_LARGE buffer of approximately 16 MB. It appends the username, separator, hash, and plaintext using memcpy without validating the accumulated length against buffer capacity. An attacker who supplies a crafted hash file with an oversized username can trigger an out-of-bounds write when hashcat runs with --username --show. The result is heap memory corruption and a process crash.
Critical Impact
A local attacker can corrupt heap memory in hashcat via a malicious hash file, leading to process crash and potential memory corruption during password auditing workflows.
Affected Products
- hashcat versions through 7.1.2
- hashcat src/outfile.coutfile_write() function
- Deployments invoking hashcat with --username --show on untrusted hash files
Discovery Timeline
- 2026-08-22 - CVE-2026-68768 published to NVD
- 2026-08-24 - Last updated in NVD database
Technical Details for CVE-2026-68768
Vulnerability Analysis
The defect resides in the output-assembly path of hashcat's outfile_write() function in src/outfile.c. The function targets a stack or heap buffer sized to HCBUFSIZ_LARGE (roughly 16 MB) and appends four fields sequentially: username, separator, hash, and recovered plaintext. Each append uses memcpy with lengths derived from attacker-controlled input. The function never checks whether the running total plus the next field length remains within the buffer capacity before copying. When the username occupies nearly the entire buffer, subsequent copies of the separator, hash, and plaintext write past the allocation boundary. The classic buffer overflow ([CWE-120]) corrupts adjacent heap metadata and causes the process to abort or behave unpredictably.
Root Cause
The root cause is missing length validation before memcpy operations in outfile_write(). The function trusts that the concatenation of variable-length fields will fit within HCBUFSIZ_LARGE. Because username length is read from the input hash file without a hard cap relative to remaining buffer space, an oversized username defeats the implicit size assumption. See the referenced source at Hashcat outfile.c lines 654-668 and the upstream commit fixing the flaw.
Attack Vector
Exploitation requires local access and user interaction. An attacker crafts a hash file containing a username long enough to nearly fill the 16 MB output buffer. The victim then runs hashcat with --username --show against that file. During output assembly, the appended separator, hash, and plaintext overflow the buffer and corrupt heap memory. The primary observed outcome is a process crash. Full code execution has not been demonstrated in public references. Additional context is available in the VulnCheck advisory and Hashcat Issue #4740.
Detection Methods for CVE-2026-68768
Indicators of Compromise
- Unexpected crashes or SIGABRT from the hashcat binary during --show operations
- Hash files containing username fields exceeding several megabytes in length
- Core dumps referencing outfile_write in the call stack
Detection Strategies
- Static inspection of hash input files to flag entries with abnormally long username fields relative to typical credential formats
- Runtime monitoring for hashcat process termination signals correlated with --username --show command-line arguments
- File integrity monitoring on hash file sources ingested by automated password-audit pipelines
Monitoring Recommendations
- Log all invocations of hashcat with full command-line arguments and originating user context
- Alert on hashcat processes that terminate abnormally, especially on shared audit hosts
- Track the provenance of hash files fed into password-recovery workflows to identify untrusted sources
How to Mitigate CVE-2026-68768
Immediate Actions Required
- Upgrade hashcat past commit 68f56a2d8712867a8520bf4dcf07f6145c23df89 when a tagged release incorporating the fix is available
- Restrict hashcat execution to hash files from trusted, validated sources
- Avoid combining --username with --show on files supplied by untrusted parties until patched
Patch Information
The upstream fix is available in the hashcat repository at commit 68f56a2. The patch adds bounds checks to outfile_write() so that field concatenation cannot exceed the HCBUFSIZ_LARGE buffer. Track the hashcat repository for the next tagged release containing this fix.
Workarounds
- Pre-validate hash files and reject any record where the username field exceeds a reasonable maximum (for example, 1024 bytes)
- Run hashcat inside a sandbox or container to contain crash and memory-corruption impact
- Disable the --username --show combination in wrapper scripts until the patched release is deployed
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
