CVE-2025-2177: Zapping-vbi Zvbi RCE Vulnerability

CVE-2025-2177 Overview

CVE-2025-2177 is an integer overflow vulnerability in libzvbi versions up to 0.2.43. The flaw resides in the vbi_search_new function within src/search.c. Attackers can trigger the overflow by manipulating the pat_len argument, which leads to memory corruption in downstream heap allocations. The vulnerability is remotely exploitable and the exploit has been publicly disclosed. The maintainers of zvbi released version 0.2.44 to address the issue via commit ca1672134b3e2962cd392212c73f44f8f4cb489f. This weakness is tracked under [CWE-190] Integer Overflow and [CWE-189] Numeric Errors.

Critical Impact
Remote attackers can trigger an integer overflow in vbi_search_new that leads to a heap-based memory corruption condition, affecting confidentiality, integrity, and availability of applications using libzvbi.

Affected Products

zapping-vbi zvbi versions up to and including 0.2.43
Applications and libraries linking against vulnerable libzvbi builds
Linux distributions packaging libzvbi prior to 0.2.44

Discovery Timeline

2025-03-11 - CVE-2025-2177 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-2177

Vulnerability Analysis

The vulnerability resides in libzvbi, a library that decodes and processes Vertical Blanking Interval (VBI) data such as Teletext and Closed Caption content. The vbi_search_new function in src/search.c accepts a pattern length parameter (pat_len) supplied by the caller. When pat_len is set to a sufficiently large value, arithmetic performed to compute allocation sizes wraps around the unsigned integer boundary. This produces a smaller-than-expected allocation, which downstream code subsequently treats as if it were the requested larger size. The result is a heap out-of-bounds write when pattern data is copied into the undersized buffer. The patch also hardens src/conv.c and src/io-sim.c, where similar unchecked size arithmetic could lead to heap overflows in buffer-extension paths.

Root Cause

The root cause is missing validation of arithmetic used to size heap allocations. The affected code paths compute buffer sizes by adding user-influenced values without verifying that the result exceeds the original operand, a standard pattern for detecting unsigned integer wrap. Because libzvbi processes untrusted media streams and search patterns, an attacker-controlled length feeds directly into allocator size arguments.

Attack Vector

The attack vector is network-adjacent. An attacker supplies crafted input that causes the calling application to invoke vbi_search_new with an oversized pat_len. Because libzvbi is embedded in media players, streaming utilities, and captioning tools, exploitation typically requires processing a malicious media stream, subtitle track, or search query. No authentication or user interaction is required beyond triggering the parsing path.

// Patch excerpt: src/io-sim.c - unsigned overflow check before extend_buffer
		if (b->size >= b->capacity) {
-			if (!extend_buffer (b, b->capacity + 256))
+			unsigned int check_buffer_size = (b->capacity + 256);
+			if (b->capacity > check_buffer_size)
+				return FALSE;
+			if (!extend_buffer (b, check_buffer_size))
 				return FALSE;
		}
// Source: https://github.com/zapping-vbi/zvbi/commit/ca1672134b3e2962cd392212c73f44f8f4cb489f

Detection Methods for CVE-2025-2177

Indicators of Compromise

Unexpected crashes or SIGSEGV signals in processes linking against libzvbi when parsing VBI, Teletext, or caption streams
Heap corruption traces (malloc/free assertions, glibc double free or corruption messages) originating from vbi_search_new, src/conv.c, or src/io-sim.c call paths
Media files or streams with abnormally large search pattern or buffer size fields

Detection Strategies

Inventory endpoints and servers for installed libzvbi package versions and flag any build below 0.2.44
Instrument test builds with AddressSanitizer (ASan) to identify heap-buffer-overflow conditions during fuzzing of vbi_search_new
Correlate crash telemetry from media-processing applications with the presence of vulnerable libzvbi versions

Monitoring Recommendations

Monitor package management logs for installations or downgrades of libzvbi below 0.2.44
Alert on repeated crashes of media-processing services on the same host, which may indicate exploitation attempts
Track file integrity for libzvbi shared objects to detect unauthorized replacement with vulnerable versions

How to Mitigate CVE-2025-2177

Immediate Actions Required

Upgrade libzvbi to version 0.2.44 or later on all affected systems
Rebuild and redistribute any statically linked applications that bundle vulnerable libzvbi code
Restrict processing of untrusted VBI, Teletext, or caption streams until patched builds are deployed

Patch Information

The fix is available in zvbi release v0.2.44 and applied via commit ca1672134b3e2962cd392212c73f44f8f4cb489f. Additional context is provided in the GitHub Security Advisory GHSA-g7cg-7gw9-v8cf. The patch adds overflow checks before allocation-sizing arithmetic in src/conv.c, src/io-sim.c, and src/search.c.

Workarounds

Disable or sandbox applications that invoke libzvbi search or VBI-decoding functions when patching is not immediately possible
Restrict input sources to trusted media streams and enforce input size limits at the application layer
Run vulnerable processes under a least-privilege account and seccomp/AppArmor profile to limit blast radius

bash

# Verify installed libzvbi version on Debian/Ubuntu systems
dpkg -l | grep libzvbi

# Upgrade to a patched version once distribution packages are available
sudo apt-get update && sudo apt-get install --only-upgrade libzvbi0

# Build from source (recommended when distribution packages lag)
git clone https://github.com/zapping-vbi/zvbi.git
cd zvbi && git checkout v0.2.44
./autogen.sh && ./configure && make && sudo make install