CVE-2025-59777 Overview
CVE-2025-59777 is a NULL pointer dereference vulnerability [CWE-476] in GNU libmicrohttpd versions 1.0.2 and earlier. GNU libmicrohttpd is a small C library used to embed HTTP server functionality into applications. A remote, unauthenticated attacker can trigger the flaw by sending a specially crafted packet, causing the embedded HTTP server to crash. The result is a denial-of-service (DoS) condition that disables availability of any application or service relying on the library. The maintainers addressed the issue in commit ff13abc1c1d7d2b30d69d5c0bd4a237e1801c50b on the master branch of the libmicrohttpd Git repository, after the v1.0.2 tag.
Critical Impact
A single crafted HTTP packet sent over the network can crash any service built on GNU libmicrohttpd v1.0.2 or earlier, with no authentication or user interaction required.
Affected Products
- GNU libmicrohttpd versions 1.0.2 and earlier
- Applications and appliances embedding vulnerable libmicrohttpd builds
- GNUnet and downstream projects shipping pre-ff13abc library binaries
Discovery Timeline
- 2025-11-10 - CVE-2025-59777 published to NVD
- 2025-11-14 - Last updated in NVD database
Technical Details for CVE-2025-59777
Vulnerability Analysis
The defect is a NULL pointer dereference inside GNU libmicrohttpd's HTTP request handling path. When the library processes an attacker-supplied packet that violates assumed parser invariants, a pointer that should reference an allocated structure remains NULL. The subsequent dereference forces a segmentation fault in the server process. Because libmicrohttpd typically runs in-process as the HTTP front end, the crash terminates the host application rather than a worker thread. The maintainers fixed the issue in commit ff13abc after the v1.0.2 release, indicating no tagged release currently contains the fix at the time of publication.
Root Cause
The root cause is the absence of a NULL check on a pointer that the parser assumed would always be initialized before use. CWE-476 covers exactly this pattern: code paths that depend on a successful prior allocation or assignment without validating the resulting pointer. Malformed input drives the parser into a state where that assumption no longer holds.
Attack Vector
The vulnerability is remotely exploitable across the network with low attack complexity. The attacker needs no privileges and no user interaction. They only need network reachability to a TCP port served by a vulnerable libmicrohttpd instance. Sending the crafted packet to that listener is sufficient to terminate the process. Confidentiality and integrity are not affected; the impact is limited to availability.
No public proof-of-concept exploit is currently listed in the references, and the issue is not present in the CISA Known Exploited Vulnerabilities catalog. Technical details are available in the GNUnet commit ff13abc and the JVN vulnerability report JVN#76719218.
Detection Methods for CVE-2025-59777
Indicators of Compromise
- Unexpected termination or restart of processes linking against libmicrohttpd, with signal SIGSEGV recorded in dmesg, journalctl, or core dump logs.
- HTTP listeners on the affected host becoming unresponsive immediately after receiving inbound traffic from an untrusted source.
- Core files referencing a NULL address dereference inside libmicrohttpd symbols in stack traces.
Detection Strategies
- Inventory all installed and statically linked versions of GNU libmicrohttpd and flag any build at or below 1.0.2 that does not include commit ff13abc.
- Correlate web server crash events with preceding inbound HTTP requests to identify probe attempts targeting embedded HTTP services.
- Deploy network monitoring rules that alert on malformed HTTP requests directed at ports hosting libmicrohttpd-based services.
Monitoring Recommendations
- Enable systemd or process supervisor metrics that track unplanned restarts of services embedding libmicrohttpd.
- Forward kernel segfault messages and application core dump events to a centralized logging or SIEM platform for review.
- Track upstream advisories from the GNU libmicrohttpd project and downstream distribution security trackers for backport availability.
How to Mitigate CVE-2025-59777
Immediate Actions Required
- Rebuild GNU libmicrohttpd from the master branch including commit ff13abc1c1d7d2b30d69d5c0bd4a237e1801c50b and redeploy dependent applications.
- Restrict network exposure of libmicrohttpd-based listeners to trusted networks until a patched build is in place.
- Identify and patch statically linked binaries; library updates alone will not fix applications that bundled the vulnerable source.
Patch Information
The fix is committed as ff13abc1c1d7d2b30d69d5c0bd4a237e1801c50b on the libmicrohttpd master branch, after the v1.0.2 tag. Administrators should track the project's next tagged release or apply the commit directly when rebuilding. Refer to the upstream commit for the exact change set.
Workarounds
- Place vulnerable services behind a hardened reverse proxy that validates and normalizes HTTP requests before forwarding traffic.
- Apply firewall or access control list rules to limit inbound connections to libmicrohttpd ports to known administrative sources.
- Configure service supervisors to auto-restart crashed processes to reduce dwell time of the DoS condition while patching is in progress.
# Configuration example: rebuild libmicrohttpd from patched master
git clone https://git.gnunet.org/libmicrohttpd.git
cd libmicrohttpd
git checkout ff13abc1c1d7d2b30d69d5c0bd4a237e1801c50b
./bootstrap
./configure --prefix=/usr/local
make && sudo make install
sudo ldconfig
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